Единый http сервис на одном порту

README.md

@@ -40,6 +40,7 @@ PLBA (`Platform Runtime for Business Applications`) - это runtime-слой д
 - `health` (`HealthRegistry`) - агрегирование здоровья воркеров и дополнительных компонентов.
 - `workflow` (`WorkflowEngine` и persistence-слой) - исполнение шагов бизнес-процесса с переходами и фиксацией состояния.
 - `control plane` (`ControlPlaneService`, `HttpControlChannel`) - внешние health/action endpoints.
+- `application HTTP` (`ApplicationHttpService`, `HttpApplicationChannel`) - пользовательские HTTP routes бизнес-приложения.
 - `queue` (`InMemoryTaskQueue`) - локальный in-memory буфер как утилита прикладного уровня.
 
 ## 3. Архитектура
@@ -89,6 +90,7 @@ classDiagram
     class HealthRegistry
     class TraceService
     class ControlPlaneService
+    class ApplicationHttpService
     class WorkflowRuntimeFactory
     class WorkflowEngine
     class WorkflowPersistence
@@ -106,6 +108,7 @@ classDiagram
     RuntimeManager --> TraceService
     RuntimeManager --> WorkerSupervisor
     RuntimeManager --> ControlPlaneService
+    RuntimeManager --> ApplicationHttpService
 
     WorkerSupervisor --> Worker
     Worker --> Routine : invokes
@@ -127,7 +130,8 @@ classDiagram
 - Реализация: контракт `app_runtime.contracts.application.ApplicationModule`, регистрация через `app_runtime.core.registration.ModuleRegistry`.
 - Как работает / API / вызовы / таблицы:
   - API: `name`, `register(registry)`.
-  - Типичные вызовы: `registry.add_worker(worker)`, `registry.add_health_contributor(contributor)`.
+- Типичные вызовы: `registry.add_worker(worker)`, `registry.add_health_contributor(contributor)`.
+- Для HTTP-модулей: `registry.add_http_routes(registrar)`.
   - `RuntimeManager.register_module()` вызывает `module.register(...)` и добавляет имя модуля в снимок runtime.
   - В БД напрямую не пишет.
 - Типовая схема использования:
@@ -314,7 +318,87 @@ with traces.open_context(alias="email:123", kind="email") as message_trace_id:
   - Producer в рутине кладет элементы через `put`.
   - Consumer-воркер извлекает через `get(timeout)` и обрабатывает.
 
-## 5. MVP бизнес-приложения
+## 5. Application HTTP
+`PLBA` поддерживает прикладной HTTP-слой для пользовательских страниц и API бизнес-приложения. По умолчанию он отделён от `control plane`, но при необходимости можно опубликовать control routes и business routes через один HTTP channel.
+
+`Control Plane` и `Application HTTP` обслуживают разные контуры:
+- `Control Plane` используется для `/health`, `/actions/*`, `/traces/*`.
+- `Application HTTP` используется для бизнес-маршрутов приложения, например `/estimate`, `/estimate/api/tasks`, `/api/orders`.
+
+### Основные компоненты
+- `ApplicationHttpService` управляет lifecycle прикладного HTTP на уровне runtime.
+- `HttpApplicationChannel` поднимает отдельный `FastAPI` app через `uvicorn`.
+- `HttpRouteRegistrar` регистрирует пользовательские routes и получает `ServiceContainer`.
+- `HttpApplicationAppFactory` собирает `FastAPI(title="PLBA Application API")`, middleware и routes.
+- `UnifiedHttpService` собирает один `FastAPI` app с control routes (`/health`, `/actions/*`, `/traces/*`) и application routes.
+
+### Минимальный пример
+```python
+from fastapi import FastAPI, File, UploadFile
+from fastapi.responses import HTMLResponse
+from plba import ApplicationModule, HttpApplicationChannel, create_runtime
+
+
+class DemoRoutes:
+    def register(self, app: FastAPI, services) -> None:
+        @app.get("/demo")
+        async def demo_page():
+            return HTMLResponse("<h1>Demo</h1>")
+
+        @app.post("/demo/api/tasks")
+        async def create_task(file: UploadFile = File(...)):
+            payload = await file.read()
+            return {"filename": file.filename, "size": len(payload)}
+
+
+class DemoModule(ApplicationModule):
+    @property
+    def name(self) -> str:
+        return "demo"
+
+    def register(self, registry) -> None:
+        registry.add_http_routes(DemoRoutes())
+
+
+runtime = create_runtime(DemoModule(), config_path="config.yml")
+runtime.application_http.register_channel(
+    HttpApplicationChannel(host="0.0.0.0", port=15000, timeout=5)
+)
+runtime.start()
+```
+
+После старта runtime приложение будет обслуживать:
+- `GET /demo`
+- `POST /demo/api/tasks`
+
+### Единый HTTP API
+Если бизнес-приложению нужен один опубликованный порт для control и application routes, передайте `UnifiedHttpService` как `application_http`:
+
+```python
+from plba import HttpApplicationChannel, RuntimeManager, UnifiedHttpService
+
+runtime = RuntimeManager(application_http=UnifiedHttpService())
+runtime.application_http.register_channel(
+    HttpApplicationChannel(host="0.0.0.0", port=15000, timeout=5)
+)
+```
+
+Старый режим с отдельными `ControlPlaneService` и `ApplicationHttpService` остаётся доступен и работает как раньше.
+
+### Типовые сценарии
+- `Web UI для фоновых задач`: список задач, запуск, статус, cancel, download result.
+- `Внутренний REST API`: например `POST /jobs`, `GET /jobs/{id}`, `POST /jobs/{id}/cancel`.
+- `Файловый шлюз`: загрузка входного файла, асинхронная обработка через worker, скачивание результата.
+- `Webhook endpoint`: прием callback от внешней системы и передача события в worker pipeline.
+
+### Ограничения и рекомендации
+- По умолчанию держите business routes и `control plane` раздельно; используйте `UnifiedHttpService`, когда один опубликованный порт является явным эксплуатационным требованием.
+- Держите бизнес-логику в сервисах, а handlers используйте как тонкий HTTP-адаптер.
+- Runtime предоставляет доступ к зависимостям через `services`, поэтому handlers не должны зависеть от `RuntimeManager`.
+- В первой версии `Application HTTP` не решает auth, static files, шаблонизаторы, websocket и OpenAPI customization.
+- Для публичного доступа выносите auth, TLS и reverse proxy на внешний ingress.
+
+## 6. MVP бизнес-приложения
 Минимальная конфигурация запуска:
 1. Создать один `ApplicationModule`.
 2. В модуле собрать одну `Routine` и один `Worker` (1 worker -> 1 routine).
@@ -374,4 +458,4 @@ runtime = create_runtime(DemoModule(), config_path="config.yml")
 runtime.start()
 ```
 
-Для production-сценария после MVP обычно добавляют `tracing`, `health contributors`, `workflow` и HTTP control plane, но базовый запуск не требует этих расширений.
+Для production-сценария после MVP обычно добавляют `tracing`, `health contributors`, `workflow`, HTTP control plane и при необходимости `application HTTP`, но базовый запуск не требует этих расширений.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "plba"
-version = "0.3.4"
+version = "0.4.0"
 description = "Platform runtime for business applications"
 readme = "README.md"
 requires-python = ">=3.11"
@@ -12,9 +12,10 @@ dependencies = [
     "fastapi>=0.129.0",
     "PyMySQL>=1.1",
     "PyYAML>=6.0.3",
+    "python-multipart>=0.0.9",
     "uvicorn>=0.41.0",
 ]
-
+ 
 [tool.setuptools.packages.find]
 where = ["src"]
 

src/app_runtime/contracts/trace.py

@@ -92,8 +92,14 @@ class TraceLogView:
     parent_id: str | None
     child_ids: tuple[str, ...] = ()
     records: tuple[TraceLogRecord, ...] = ()
+    ancestors: tuple[TraceLogView, ...] = ()
 
 
 class TraceLogReader(Protocol):
-    def read_trace(self, trace_id: str, levels: tuple[TraceLevel, ...]) -> TraceLogView | None:
+    def read_trace(
+        self,
+        trace_id: str,
+        levels: tuple[TraceLevel, ...],
+        ancestor_depth: int | None = 0,
+    ) -> TraceLogView | None:
         """Load trace context and filtered log records."""

src/app_runtime/control/action_responder.py

@@ -0,0 +1,46 @@
+from __future__ import annotations
+
+import asyncio
+
+from fastapi.responses import JSONResponse
+
+from app_runtime.control.base import ControlActionRequest, ControlActionSet
+
+
+class ControlActionResponder:
+    def __init__(self, actions: ControlActionSet, timeout: int) -> None:
+        self._actions = actions
+        self._timeout = timeout
+
+    async def respond(
+        self,
+        action: str,
+        _client_source: str = "unknown",
+        request: ControlActionRequest | None = None,
+    ) -> JSONResponse:
+        callbacks = {
+            "start": self._actions.start,
+            "stop": self._actions.stop,
+            "status": self._actions.status,
+        }
+        callback = callbacks.get(action)
+        if callback is None:
+            return JSONResponse(content={"status": "error", "detail": f"unsupported action: {action}"}, status_code=404)
+        action_request = request or ControlActionRequest()
+        action_timeout = self._action_timeout(action, action_request)
+        try:
+            detail = await asyncio.wait_for(callback(action_request), timeout=action_timeout)
+        except asyncio.TimeoutError:
+            return JSONResponse(
+                content={"status": "accepted", "detail": f"{action} operation is still in progress"},
+                status_code=202,
+            )
+        except Exception as exc:
+            return JSONResponse(content={"status": "error", "detail": str(exc)}, status_code=500)
+        return JSONResponse(content={"status": "ok", "detail": detail or f"{action} action accepted"}, status_code=200)
+
+    def _action_timeout(self, action: str, request: ControlActionRequest) -> float:
+        base_timeout = max(float(self._timeout), 10.0) if action in {"start", "stop"} else float(self._timeout)
+        if action != "stop" or request.wait is False or request.timeout is None:
+            return base_timeout
+        return max(base_timeout, float(request.timeout) + 1.0)

src/app_runtime/control/base.py

@@ -19,14 +19,15 @@ class ControlActionRequest:
 ActionResult = str | dict[str, object]
 ActionHandler = Callable[[ControlActionRequest], Awaitable[ActionResult]]
 HealthHandler = Callable[[], Awaitable[HealthPayload]]
-TraceResponseFormat = Literal["json", "text"]
+TraceResponseFormat = Literal["json", "text", "html"]
 
 
 @dataclass(slots=True)
 class TraceQueryRequest:
     levels: tuple[TraceLevel, ...] = ("ERROR", "WARNING", "INFO")
     include_attrs_json: bool = False
-    response_format: TraceResponseFormat = "text"
+    response_format: TraceResponseFormat = "html"
+    ancestor_depth: int | None = 0
 
 
 TraceLookupHandler = Callable[[str, TraceQueryRequest], Awaitable[TraceLogView]]

src/app_runtime/control/http_app.py

@@ -1,22 +1,30 @@
 from __future__ import annotations
 
-import json
 import logging
 import time
 from collections.abc import Awaitable, Callable
-from typing import cast
 
 from fastapi import FastAPI, Request
-from fastapi.responses import JSONResponse, PlainTextResponse
+from fastapi.responses import JSONResponse
 
 from app_runtime.control.base import ControlActionRequest, TraceQueryRequest
-from app_runtime.contracts.trace import TraceLevel, TraceLogView
+from app_runtime.control.trace_presenter import TraceRequestParser, TraceResponseRenderer
+from app_runtime.contracts.trace import TraceLogView
 from app_runtime.core.types import HealthPayload
 
 LOGGER = logging.getLogger(__name__)
 
 
 class HttpControlAppFactory:
+    def __init__(
+        self,
+        *,
+        trace_request_parser: TraceRequestParser | None = None,
+        trace_response_renderer: TraceResponseRenderer | None = None,
+    ) -> None:
+        self._trace_request_parser = trace_request_parser or TraceRequestParser()
+        self._trace_response_renderer = trace_response_renderer or TraceResponseRenderer()
+
     def create(
         self,
         health_provider: Callable[[], Awaitable[HealthPayload]],
@@ -55,7 +63,7 @@ class HttpControlAppFactory:
             if trace_provider is None:
                 return JSONResponse(content={"status": "error", "detail": "trace lookup is not configured"}, status_code=503)
             try:
-                trace_request = self._trace_request(request)
+                trace_request = self._trace_request_parser.parse(request)
             except ValueError as exc:
                 return JSONResponse(content={"status": "error", "detail": str(exc)}, status_code=400)
             try:
@@ -64,7 +72,7 @@ class HttpControlAppFactory:
                 return JSONResponse(content={"status": "error", "detail": f"trace not found: {traceid}"}, status_code=404)
             except RuntimeError as exc:
                 return JSONResponse(content={"status": "error", "detail": str(exc)}, status_code=503)
-            return self._trace_response(payload, trace_request)
+            return self._trace_response_renderer.render(payload, trace_request)
 
         return app
 
@@ -106,65 +114,3 @@ class HttpControlAppFactory:
         if value < 0:
             raise ValueError(f"query parameter must be >= 0: {name}={raw_value}")
         return value
-
-    def _trace_request(self, request: Request) -> TraceQueryRequest:
-        raw_levels = request.query_params.get("levels")
-        raw_format = request.query_params.get("format", "text")
-        response_format = raw_format.strip().lower()
-        if response_format not in {"json", "text"}:
-            raise ValueError(f"unsupported trace format: {raw_format}")
-        return TraceQueryRequest(
-            levels=self._trace_levels(raw_levels),
-            include_attrs_json=self._bool_param(request, "attrs_json") or False,
-            response_format=response_format,
-        )
-
-    def _trace_levels(self, raw_levels: str | None) -> tuple[TraceLevel, ...]:
-        if raw_levels is None:
-            return ("ERROR", "WARNING", "INFO")
-        parts = [item.strip().upper() for item in raw_levels.split(",")]
-        levels = tuple(item for item in parts if item)
-        if not levels:
-            raise ValueError("trace levels must not be empty")
-        unsupported = [level for level in levels if level not in {"DEBUG", "INFO", "WARNING", "ERROR"}]
-        if unsupported:
-            raise ValueError(f"unsupported trace levels: {', '.join(unsupported)}")
-        return cast(tuple[TraceLevel, ...], levels)
-
-    def _trace_response(self, trace_view: TraceLogView, request: TraceQueryRequest) -> JSONResponse | PlainTextResponse:
-        if request.response_format == "json":
-            return JSONResponse(
-                content={
-                    "trace_id": trace_view.trace_id,
-                    "parent_id": trace_view.parent_id or "",
-                    "child_ids": list(trace_view.child_ids),
-                    "messages": [record.as_dict(include_attrs_json=request.include_attrs_json) for record in trace_view.records],
-                }
-            )
-        lines = [
-            f"trace_id: {trace_view.trace_id}",
-            f"parent_id: {trace_view.parent_id or ''}",
-        ]
-        lines.extend(self._child_id_lines(trace_view.child_ids))
-        lines.append("--------------------------------------------------")
-        previous_step: str | None = None
-        for record in trace_view.records:
-            current_step = str(record.step or "")
-            if previous_step is None:
-                lines.append(f"step: {current_step}")
-            elif current_step != previous_step:
-                lines.append("--------------------------------------------------")
-                lines.append(f"step: {current_step}")
-            previous_step = current_step
-            line = record.message
-            if request.include_attrs_json:
-                line = f"{line}, {json.dumps(record.attrs_json, ensure_ascii=False, separators=(',', ':'))}"
-            lines.append(line)
-        return PlainTextResponse(content="\n".join(lines))
-
-    def _child_id_lines(self, child_ids: tuple[str, ...]) -> list[str]:
-        lines = ["child_ids:"]
-        if not child_ids:
-            return lines
-        lines.extend(f" - {child_id}" for child_id in child_ids)
-        return lines

src/app_runtime/control/http_channel.py

@@ -4,6 +4,7 @@ import asyncio
 
 from fastapi.responses import JSONResponse
 
+from app_runtime.control.action_responder import ControlActionResponder
 from app_runtime.control.base import ControlActionRequest, ControlActionSet, ControlChannel, TraceQueryRequest
 from app_runtime.contracts.trace import TraceLogView
 from app_runtime.control.http_app import HttpControlAppFactory
@@ -16,9 +17,11 @@ class HttpControlChannel(ControlChannel):
         self._runner = UvicornThreadRunner(host, port, timeout)
         self._factory = HttpControlAppFactory()
         self._actions: ControlActionSet | None = None
+        self._action_responder: ControlActionResponder | None = None
 
     async def start(self, actions: ControlActionSet) -> None:
         self._actions = actions
+        self._action_responder = ControlActionResponder(actions, self._timeout)
         app = self._factory.create(self._health_response, self._action_response, self._trace_response)
         await self._runner.start(app)
 
@@ -40,34 +43,14 @@ class HttpControlChannel(ControlChannel):
         _client_source: str = "unknown",
         request: ControlActionRequest | None = None,
     ) -> JSONResponse:
-        if self._actions is None:
+        if self._action_responder is None:
-            return JSONResponse(content={"status": "error", "detail": f"{action} handler is not configured"}, status_code=404)
+            if self._actions is None:
-        callbacks = {
+                return JSONResponse(
-            "start": self._actions.start,
+                    content={"status": "error", "detail": f"{action} handler is not configured"},
-            "stop": self._actions.stop,
+                    status_code=404,
-            "status": self._actions.status,
+                )
-        }
+            self._action_responder = ControlActionResponder(self._actions, self._timeout)
-        callback = callbacks.get(action)
+        return await self._action_responder.respond(action, _client_source, request)
-        if callback is None:
-            return JSONResponse(content={"status": "error", "detail": f"unsupported action: {action}"}, status_code=404)
-        action_request = request or ControlActionRequest()
-        action_timeout = self._action_timeout(action, action_request)
-        try:
-            detail = await asyncio.wait_for(callback(action_request), timeout=action_timeout)
-        except asyncio.TimeoutError:
-            return JSONResponse(
-                content={"status": "accepted", "detail": f"{action} operation is still in progress"},
-                status_code=202,
-            )
-        except Exception as exc:
-            return JSONResponse(content={"status": "error", "detail": str(exc)}, status_code=500)
-        return JSONResponse(content={"status": "ok", "detail": detail or f"{action} action accepted"}, status_code=200)
-
-    def _action_timeout(self, action: str, request: ControlActionRequest) -> float:
-        base_timeout = max(float(self._timeout), 10.0) if action in {"start", "stop"} else float(self._timeout)
-        if action != "stop" or request.wait is False or request.timeout is None:
-            return base_timeout
-        return max(base_timeout, float(request.timeout) + 1.0)
 
     async def _trace_response(self, trace_id: str, request: TraceQueryRequest) -> TraceLogView:
         if self._actions is None or self._actions.trace_lookup is None:

src/app_runtime/control/http_runner.py

@@ -8,10 +8,11 @@ from uvicorn import Config, Server
 
 
 class UvicornThreadRunner:
-    def __init__(self, host: str, port: int, timeout: int) -> None:
+    def __init__(self, host: str, port: int, timeout: int, *, thread_name: str = "plba-http-control") -> None:
         self._host = host
         self._port = port
         self._timeout = timeout
+        self._thread_name = thread_name
         self._server: Server | None = None
         self._thread: Thread | None = None
         self._error: BaseException | None = None
@@ -22,7 +23,7 @@ class UvicornThreadRunner:
         self._error = None
         config = Config(app=app, host=self._host, port=self._port, log_level="warning")
         self._server = Server(config)
-        self._thread = Thread(target=self._serve, name="plba-http-control", daemon=True)
+        self._thread = Thread(target=self._serve, name=self._thread_name, daemon=True)
         self._thread.start()
         await self._wait_until_started()
 

src/app_runtime/control/trace_presenter.py

@@ -0,0 +1,293 @@
+from __future__ import annotations
+
+import json
+from html import escape
+from urllib.parse import urlencode
+
+from fastapi import Request
+from fastapi.responses import HTMLResponse, JSONResponse, PlainTextResponse, Response
+
+from app_runtime.control.base import TraceQueryRequest
+from app_runtime.contracts.trace import TraceLevel, TraceLogRecord, TraceLogView
+
+
+TRACE_SECTION_SEPARATOR = "=" * 30
+
+
+class TraceRequestParser:
+    def parse(self, request: Request) -> TraceQueryRequest:
+        raw_levels = request.query_params.get("levels")
+        raw_format = request.query_params.get("format", "html")
+        response_format = raw_format.strip().lower()
+        if response_format not in {"json", "text", "html"}:
+            raise ValueError(f"unsupported trace format: {raw_format}")
+        return TraceQueryRequest(
+            levels=self._trace_levels(raw_levels),
+            include_attrs_json=self._bool_param(request, "attrs_json") or False,
+            response_format=response_format,
+            ancestor_depth=self._ancestor_depth(request),
+        )
+
+    def _trace_levels(self, raw_levels: str | None) -> tuple[TraceLevel, ...]:
+        if raw_levels is None:
+            return ("ERROR", "WARNING", "INFO")
+        parts = [item.strip().upper() for item in raw_levels.split(",")]
+        levels = tuple(item for item in parts if item)
+        if not levels:
+            raise ValueError("trace levels must not be empty")
+        unsupported = [level for level in levels if level not in {"DEBUG", "INFO", "WARNING", "ERROR"}]
+        if unsupported:
+            raise ValueError(f"unsupported trace levels: {', '.join(unsupported)}")
+        return levels
+
+    def _bool_param(self, request: Request, name: str) -> bool | None:
+        raw_value = request.query_params.get(name)
+        if raw_value is None:
+            return None
+        normalized = raw_value.strip().lower()
+        if normalized in {"1", "true", "yes", "on"}:
+            return True
+        if normalized in {"0", "false", "no", "off"}:
+            return False
+        raise ValueError(f"invalid boolean query parameter: {name}={raw_value}")
+
+    def _ancestor_depth(self, request: Request) -> int | None:
+        raw_value = request.query_params.get("ancestor_depth")
+        if raw_value is None:
+            return 0
+        normalized = raw_value.strip().lower()
+        if normalized == "all":
+            return None
+        try:
+            value = int(normalized)
+        except ValueError as exc:
+            raise ValueError(f"invalid ancestor depth query parameter: ancestor_depth={raw_value}") from exc
+        if value < 0:
+            raise ValueError(f"query parameter must be >= 0: ancestor_depth={raw_value}")
+        return value
+
+
+class TraceResponseRenderer:
+    def render(self, trace_view: TraceLogView, request: TraceQueryRequest) -> Response:
+        if request.response_format == "json":
+            return self._render_json(trace_view, request)
+        if request.response_format == "html":
+            return self._render_html(trace_view, request)
+        return self._render_text(trace_view, request)
+
+    def _render_json(self, trace_view: TraceLogView, request: TraceQueryRequest) -> JSONResponse:
+        return JSONResponse(
+            content={
+                "trace_id": trace_view.trace_id,
+                "parent_id": trace_view.parent_id or "",
+                "child_ids": list(trace_view.child_ids),
+                "messages": [record.as_dict(include_attrs_json=request.include_attrs_json) for record in trace_view.records],
+                "ancestors": [self._trace_payload(view, request) for view in trace_view.ancestors],
+            }
+        )
+
+    def _render_text(self, trace_view: TraceLogView, request: TraceQueryRequest) -> PlainTextResponse:
+        lineage = [*trace_view.ancestors, trace_view]
+        lines = self._text_trace_summary_lines(trace_view)
+        for index, entry in enumerate(lineage):
+            if index == 0:
+                lines.append("")
+            else:
+                lines.extend(["", ""])
+            lines.extend(self._text_trace_log_lines(entry, request))
+        return PlainTextResponse(content="\n".join(lines))
+
+    def _render_html(self, trace_view: TraceLogView, request: TraceQueryRequest) -> HTMLResponse:
+        title = escape(f"Trace {trace_view.trace_id}")
+        lines = self._html_lines(trace_view, request)
+        html = f"""<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>{title}</title>
+  <style>
+    :root {{
+      color-scheme: dark;
+      --bg: #000000;
+      --fg: #ececec;
+      --step: #ffffff;
+      --link: #66d9ef;
+      --error: #ff817d;
+      --warning: #e9ebec;
+      --info: #d6d7d9;
+      --other: #ececec;
+    }}
+    body {{
+      margin: 0;
+      background: var(--bg);
+      color: var(--fg);
+      font: 13px/1.1 "SFMono-Regular", monospace;
+    }}
+    .page {{
+      padding: 14px 16px 24px;
+    }}
+    a {{
+      color: var(--link);
+      text-decoration: underline;
+      text-underline-offset: 2px;
+    }}
+    .line {{
+      white-space: pre-wrap;
+      word-break: break-word;
+    }}
+    .msg-error {{
+      color: var(--error);
+    }}
+    .msg-warning {{
+      color: var(--warning);
+    }}
+    .msg-info {{
+      color: var(--info);
+    }}
+    .msg-debug {{
+      color: var(--other);
+    }}
+    @media (max-width: 640px) {{
+      .page {{
+        padding: 12px 12px 20px;
+      }}
+    }}
+  </style>
+</head>
+<body>
+  <div class="page">
+    {lines}
+  </div>
+</body>
+</html>"""
+        return HTMLResponse(content=html)
+
+    def _child_id_lines(self, child_ids: tuple[str, ...]) -> list[str]:
+        lines = ["child_ids:"]
+        lines.extend(f" - {child_id}" for child_id in child_ids)
+        return lines
+
+    def _text_message(self, record: TraceLogRecord, include_attrs_json: bool) -> str:
+        if not include_attrs_json:
+            return record.message
+        return f"{record.message}, {json.dumps(record.attrs_json, ensure_ascii=False, separators=(',', ':'))}"
+
+    def _trace_href(self, trace_id: str, request: TraceQueryRequest) -> str:
+        params = {
+            "format": "html",
+            "levels": ",".join(request.levels),
+            "attrs_json": "true" if request.include_attrs_json else "false",
+        }
+        if request.ancestor_depth is None:
+            params["ancestor_depth"] = "all"
+        elif request.ancestor_depth > 0:
+            params["ancestor_depth"] = str(request.ancestor_depth)
+        query = urlencode(params)
+        return f"/traces/{trace_id}?{query}"
+
+    def _html_lines(self, trace_view: TraceLogView, request: TraceQueryRequest) -> str:
+        lineage = [*trace_view.ancestors, trace_view]
+        lines = self._html_trace_summary_lines(trace_view, request)
+        for index, entry in enumerate(lineage):
+            if index == 0:
+                lines.append(self._html_plain_line(""))
+            else:
+                lines.extend([self._html_plain_line(""), self._html_plain_line("")])
+            lines.extend(self._html_trace_log_lines(entry, request))
+        return "".join(lines)
+
+    def _trace_payload(self, trace_view: TraceLogView, request: TraceQueryRequest) -> dict[str, object]:
+        return {
+            "trace_id": trace_view.trace_id,
+            "parent_id": trace_view.parent_id or "",
+            "child_ids": list(trace_view.child_ids),
+            "messages": [record.as_dict(include_attrs_json=request.include_attrs_json) for record in trace_view.records],
+        }
+
+    def _text_trace_summary_lines(self, trace_view: TraceLogView) -> list[str]:
+        return [
+            f"trace_id: {trace_view.trace_id}",
+            f"parent_id: {trace_view.parent_id or ''}",
+            *self._child_id_lines(trace_view.child_ids),
+        ]
+
+    def _text_trace_log_lines(self, trace_view: TraceLogView, request: TraceQueryRequest) -> list[str]:
+        lines = [
+            TRACE_SECTION_SEPARATOR,
+            f"trace_id: {trace_view.trace_id}",
+            "",
+        ]
+        previous_step: str | None = None
+        for record in trace_view.records:
+            current_step = str(record.step or "")
+            if previous_step is None:
+                lines.append(f"step: {current_step}")
+            elif current_step != previous_step:
+                lines.append("------------------------------")
+                lines.append(f"step: {current_step}")
+            previous_step = current_step
+            lines.append(self._text_message(record, request.include_attrs_json))
+        return lines
+
+    def _html_trace_summary_lines(self, trace_view: TraceLogView, request: TraceQueryRequest) -> list[str]:
+        return [
+            self._html_plain_line(f"trace_id: {self._trace_link(trace_view.trace_id, request)}"),
+            self._html_plain_line(f"parent_id: {self._optional_trace_link(trace_view.parent_id, request)}"),
+            self._html_plain_line("child_ids:"),
+            *(self._html_plain_line(f" - {self._trace_link(child_id, request)}") for child_id in trace_view.child_ids),
+        ]
+
+    def _html_trace_log_lines(self, trace_view: TraceLogView, request: TraceQueryRequest) -> list[str]:
+        lines = [
+            self._html_plain_line(TRACE_SECTION_SEPARATOR),
+            self._html_plain_line(f"trace_id: {self._trace_link(trace_view.trace_id, request)}"),
+            self._html_plain_line(""),
+        ]
+        previous_step: str | None = None
+        for record in trace_view.records:
+            current_step = str(record.step or "")
+            if previous_step is None:
+                lines.append(self._html_step_line(current_step))
+                lines.append(self._html_plain_line(""))
+            elif current_step != previous_step:
+                lines.append(self._html_plain_line(""))
+                lines.append(self._html_plain_line("------------------------------"))
+                lines.append(self._html_step_line(current_step))
+                lines.append(self._html_plain_line(""))
+            previous_step = current_step
+            lines.extend(self._html_message_lines(record, request.include_attrs_json))
+        return lines
+
+    def _html_message_lines(self, record: TraceLogRecord, include_attrs_json: bool) -> list[str]:
+        lines = [self._html_colored_line(self._text_message(record, include_attrs_json), record.level)]
+        return lines
+
+    def _html_plain_line(self, content: str) -> str:
+        return f"<div class=\"line\">{content or '&nbsp;'}</div>"
+
+    def _html_step_line(self, content: str) -> str:
+        return f"<div class=\"line\" style=\"color: var(--step);\">{escape(content) or '&nbsp;'}</div>"
+
+    def _html_colored_line(self, content: str, level: str) -> str:
+        level_class = self._level_class(level)
+        return f"<div class=\"line {level_class}\">{escape(content)}</div>"
+
+    def _trace_link(self, trace_id: str, request: TraceQueryRequest) -> str:
+        href = escape(self._trace_href(trace_id, request), quote=True)
+        text = escape(trace_id)
+        return f"<a href=\"{href}\">{text}</a>"
+
+    def _optional_trace_link(self, trace_id: str | None, request: TraceQueryRequest) -> str:
+        if not trace_id:
+            return ""
+        return self._trace_link(trace_id, request)
+
+    def _level_class(self, level: str) -> str:
+        if level == "ERROR":
+            return "msg-error"
+        if level == "WARNING":
+            return "msg-warning"
+        if level == "INFO":
+            return "msg-info"
+        return "msg-debug"

src/app_runtime/core/registration.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 from app_runtime.contracts.health import HealthContributor
 from app_runtime.contracts.worker import Worker
 from app_runtime.core.service_container import ServiceContainer
+from app_runtime.http.base import HttpRouteRegistrar
 
 
 class ModuleRegistry:
@@ -10,6 +11,7 @@ class ModuleRegistry:
         self.services = services
         self.workers: list[Worker] = []
         self.health_contributors: list[HealthContributor] = []
+        self.http_route_registrars: list[HttpRouteRegistrar] = []
         self.modules: list[str] = []
 
     def register_module(self, name: str) -> None:
@@ -20,3 +22,6 @@ class ModuleRegistry:
 
     def add_health_contributor(self, contributor: HealthContributor) -> None:
         self.health_contributors.append(contributor)
+
+    def add_http_routes(self, registrar: HttpRouteRegistrar) -> None:
+        self.http_route_registrars.append(registrar)

src/app_runtime/core/runtime.py

@@ -13,6 +13,7 @@ from app_runtime.core.registration import ModuleRegistry
 from app_runtime.core.service_container import ServiceContainer
 from app_runtime.core.types import HealthPayload, LifecycleState
 from app_runtime.health.registry import HealthRegistry
+from app_runtime.http.service import ApplicationHttpService
 from app_runtime.logging.manager import LogManager
 from app_runtime.tracing.reader import build_trace_log_reader
 from app_runtime.tracing.service import TraceService
@@ -32,6 +33,7 @@ class RuntimeManager:
         logs: LogManager | None = None,
         workers: WorkerSupervisor | None = None,
         control_plane: ControlPlaneService | None = None,
+        application_http: ApplicationHttpService | None = None,
     ) -> None:
         self.configuration = configuration or ConfigurationManager()
         self.services = services or ServiceContainer()
@@ -40,6 +42,7 @@ class RuntimeManager:
         self.logs = logs or LogManager()
         self.workers = workers or WorkerSupervisor()
         self.control_plane = control_plane or ControlPlaneService()
+        self.application_http = application_http or ApplicationHttpService()
         self.registry = ModuleRegistry(self.services)
         self._started = False
         self._state = LifecycleState.IDLE
@@ -67,6 +70,8 @@ class RuntimeManager:
         self.workers.start()
         if start_control_plane:
             self.control_plane.start(self)
+        self._register_application_http_routes()
+        self.application_http.start(self)
         self._started = True
         self._refresh_state()
 
@@ -75,6 +80,7 @@ class RuntimeManager:
             return
         self._state = LifecycleState.STOPPING
         self.workers.stop(timeout=timeout, force=force)
+        self.application_http.stop()
         if stop_control_plane:
             self.control_plane.stop()
         self._started = False
@@ -120,6 +126,7 @@ class RuntimeManager:
         except TimeoutError:
             return self._action_detail("runtime stop is still in progress", timed_out=True)
 
+        self.application_http.stop()
         self._refresh_state()
         if self._state == LifecycleState.STOPPED:
             self._started = False
@@ -134,7 +141,7 @@ class RuntimeManager:
         reader = build_trace_log_reader(self.traces.transport)
         if reader is None:
             raise RuntimeError("trace log reader is not configured")
-        trace_view = reader.read_trace(trace_id, request.levels)
+        trace_view = reader.read_trace(trace_id, request.levels, request.ancestor_depth)
         if trace_view is None:
             raise KeyError(trace_id)
         return trace_view
@@ -148,6 +155,7 @@ class RuntimeManager:
         self.services.register("logs", self.logs)
         self.services.register("workers", self.workers)
         self.services.register("control_plane", self.control_plane)
+        self.services.register("application_http", self.application_http)
         self._core_registered = True
 
     def _register_health_contributors(self) -> None:
@@ -161,6 +169,11 @@ class RuntimeManager:
             self.workers.register(worker)
         self._workers_registered = True
 
+    def _register_application_http_routes(self) -> None:
+        for registrar in self.registry.http_route_registrars:
+            self.application_http.register_routes(registrar)
+        self.registry.http_route_registrars.clear()
+
     def _refresh_state(self) -> None:
         lifecycle = self.workers.lifecycle_state()
 

src/app_runtime/http/__init__.py

@@ -0,0 +1,14 @@
+from app_runtime.http.base import ApplicationHttpChannel, HttpRouteRegistrar
+from app_runtime.http.http_app import HttpApplicationAppFactory
+from app_runtime.http.http_channel import HttpApplicationChannel
+from app_runtime.http.service import ApplicationHttpService
+from app_runtime.http.unified_service import UnifiedHttpService
+
+__all__ = [
+    "ApplicationHttpChannel",
+    "ApplicationHttpService",
+    "HttpApplicationAppFactory",
+    "HttpApplicationChannel",
+    "HttpRouteRegistrar",
+    "UnifiedHttpService",
+]

src/app_runtime/http/base.py

@@ -0,0 +1,23 @@
+from __future__ import annotations
+
+from abc import ABC, abstractmethod
+from typing import Protocol
+
+from fastapi import FastAPI
+
+from app_runtime.core.service_container import ServiceContainer
+
+
+class HttpRouteRegistrar(Protocol):
+    def register(self, app: FastAPI, services: ServiceContainer) -> None:
+        """Register application routes on the provided FastAPI app."""
+
+
+class ApplicationHttpChannel(ABC):
+    @abstractmethod
+    async def start(self, app: FastAPI) -> None:
+        """Start the HTTP channel with the prepared application app."""
+
+    @abstractmethod
+    async def stop(self) -> None:
+        """Stop the HTTP channel and release resources."""

src/app_runtime/http/http_app.py

@@ -0,0 +1,37 @@
+from __future__ import annotations
+
+import logging
+import time
+from collections.abc import Iterable
+
+from fastapi import FastAPI, Request
+
+from app_runtime.core.service_container import ServiceContainer
+from app_runtime.http.base import HttpRouteRegistrar
+
+LOGGER = logging.getLogger(__name__)
+
+
+class HttpApplicationAppFactory:
+    def create(self, registrars: Iterable[HttpRouteRegistrar], services: ServiceContainer) -> FastAPI:
+        app = FastAPI(title="PLBA Application API")
+        self._register_middleware(app)
+        for registrar in registrars:
+            registrar.register(app, services)
+        return app
+
+    def _register_middleware(self, app: FastAPI) -> None:
+        @app.middleware("http")
+        async def track_request(request: Request, call_next):  # type: ignore[no-untyped-def]
+            started = time.monotonic()
+            response = await call_next(request)
+            duration_ms = int((time.monotonic() - started) * 1000)
+            response.headers["X-Response-Time-Ms"] = str(duration_ms)
+            LOGGER.info(
+                "Application HTTP request handled: method=%s path=%s status=%s duration_ms=%s",
+                request.method,
+                request.url.path,
+                response.status_code,
+                duration_ms,
+            )
+            return response

src/app_runtime/http/http_channel.py

@@ -0,0 +1,21 @@
+from __future__ import annotations
+
+from fastapi import FastAPI
+
+from app_runtime.control.http_runner import UvicornThreadRunner
+from app_runtime.http.base import ApplicationHttpChannel
+
+
+class HttpApplicationChannel(ApplicationHttpChannel):
+    def __init__(self, host: str, port: int, timeout: int) -> None:
+        self._runner = UvicornThreadRunner(host, port, timeout, thread_name="plba-http-application")
+
+    async def start(self, app: FastAPI) -> None:
+        await self._runner.start(app)
+
+    async def stop(self) -> None:
+        await self._runner.stop()
+
+    @property
+    def port(self) -> int:
+        return self._runner.port

src/app_runtime/http/service.py

@@ -0,0 +1,42 @@
+from __future__ import annotations
+
+import asyncio
+from typing import TYPE_CHECKING
+
+from app_runtime.http.base import ApplicationHttpChannel, HttpRouteRegistrar
+from app_runtime.http.http_app import HttpApplicationAppFactory
+
+if TYPE_CHECKING:
+    from app_runtime.core.runtime import RuntimeManager
+
+
+class ApplicationHttpService:
+    def __init__(self, app_factory: HttpApplicationAppFactory | None = None) -> None:
+        self._channels: list[ApplicationHttpChannel] = []
+        self._registrars: list[HttpRouteRegistrar] = []
+        self._app_factory = app_factory or HttpApplicationAppFactory()
+
+    def register_channel(self, channel: ApplicationHttpChannel) -> None:
+        self._channels.append(channel)
+
+    def register_routes(self, registrar: HttpRouteRegistrar) -> None:
+        self._registrars.append(registrar)
+
+    def start(self, runtime: RuntimeManager) -> None:
+        if not self._channels:
+            return
+        asyncio.run(self._start_async(runtime))
+
+    def stop(self) -> None:
+        if not self._channels:
+            return
+        asyncio.run(self._stop_async())
+
+    async def _start_async(self, runtime: RuntimeManager) -> None:
+        app = self._app_factory.create(self._registrars, runtime.services)
+        for channel in self._channels:
+            await channel.start(app)
+
+    async def _stop_async(self) -> None:
+        for channel in reversed(self._channels):
+            await channel.stop()

src/app_runtime/http/unified_service.py

@@ -0,0 +1,68 @@
+from __future__ import annotations
+
+import asyncio
+from typing import TYPE_CHECKING
+
+from app_runtime.control.action_responder import ControlActionResponder
+from app_runtime.control.base import ControlActionSet
+from app_runtime.control.http_app import HttpControlAppFactory
+from app_runtime.http.base import ApplicationHttpChannel, HttpRouteRegistrar
+from app_runtime.http.http_app import HttpApplicationAppFactory
+
+if TYPE_CHECKING:
+    from app_runtime.core.runtime import RuntimeManager
+
+
+class UnifiedHttpService:
+    """Publish control and application routes through the same HTTP channel."""
+
+    def __init__(
+        self,
+        app_factory: HttpApplicationAppFactory | None = None,
+        control_app_factory: HttpControlAppFactory | None = None,
+        control_timeout: int = 5,
+    ) -> None:
+        self._channels: list[ApplicationHttpChannel] = []
+        self._registrars: list[HttpRouteRegistrar] = []
+        self._app_factory = app_factory or HttpApplicationAppFactory()
+        self._control_app_factory = control_app_factory or HttpControlAppFactory()
+        self._control_timeout = control_timeout
+
+    def register_channel(self, channel: ApplicationHttpChannel) -> None:
+        self._channels.append(channel)
+
+    def register_routes(self, registrar: HttpRouteRegistrar) -> None:
+        self._registrars.append(registrar)
+
+    def start(self, runtime: RuntimeManager) -> None:
+        if not self._channels:
+            return
+        asyncio.run(self._start_async(runtime))
+
+    def stop(self) -> None:
+        if not self._channels:
+            return
+        asyncio.run(self._stop_async())
+
+    async def _start_async(self, runtime: RuntimeManager) -> None:
+        app = self._app_factory.create(self._registrars, runtime.services)
+        actions = ControlActionSet(
+            health=runtime.health_status,
+            start=runtime.start_runtime,
+            stop=runtime.stop_runtime,
+            status=runtime.runtime_status,
+            trace_lookup=runtime.trace_logs,
+        )
+        action_responder = ControlActionResponder(actions, self._control_timeout)
+        control_app = self._control_app_factory.create(
+            actions.health,
+            action_responder.respond,
+            actions.trace_lookup,
+        )
+        app.router.routes.extend(control_app.router.routes)
+        for channel in self._channels:
+            await channel.start(app)
+
+    async def _stop_async(self) -> None:
+        for channel in reversed(self._channels):
+            await channel.stop()

src/app_runtime/tracing/reader.py

@@ -11,10 +11,16 @@ class MySqlTraceLogReader(TraceLogReader):
     def __init__(self, connection_factory: MySqlTraceConnectionFactory) -> None:
         self._connection_factory = connection_factory
 
-    def read_trace(self, trace_id: str, levels: tuple[TraceLevel, ...]) -> TraceLogView | None:
+    def read_trace(
+        self,
+        trace_id: str,
+        levels: tuple[TraceLevel, ...],
+        ancestor_depth: int | None = 0,
+    ) -> TraceLogView | None:
         parent_id = self._read_parent_id(trace_id)
         if parent_id is None and not self._trace_exists(trace_id):
             return None
+        ancestors = self._read_ancestors(parent_id, levels, ancestor_depth)
         child_ids = self._read_child_ids(trace_id)
         records = self._read_records(trace_id, levels)
         return TraceLogView(
@@ -22,8 +28,36 @@ class MySqlTraceLogReader(TraceLogReader):
             parent_id=parent_id,
             child_ids=tuple(child_ids),
             records=tuple(records),
+            ancestors=tuple(ancestors),
         )
 
+    def _read_ancestors(
+        self,
+        parent_id: str | None,
+        levels: tuple[TraceLevel, ...],
+        ancestor_depth: int | None,
+    ) -> list[TraceLogView]:
+        if parent_id is None or ancestor_depth == 0:
+            return []
+        remaining_depth = ancestor_depth
+        ancestors: list[TraceLogView] = []
+        current_trace_id = parent_id
+        while current_trace_id is not None and (remaining_depth is None or remaining_depth > 0):
+            current_parent_id = self._read_parent_id(current_trace_id)
+            ancestors.append(
+                TraceLogView(
+                    trace_id=current_trace_id,
+                    parent_id=current_parent_id,
+                    child_ids=tuple(self._read_child_ids(current_trace_id)),
+                    records=tuple(self._read_records(current_trace_id, levels)),
+                )
+            )
+            current_trace_id = current_parent_id
+            if remaining_depth is not None:
+                remaining_depth -= 1
+        ancestors.reverse()
+        return ancestors
+
     def _trace_exists(self, trace_id: str) -> bool:
         query = "SELECT 1 FROM trace_contexts WHERE trace_id = %s"
         with self._connection_factory.connect() as connection:

src/plba/__init__.py

@@ -15,6 +15,14 @@ from plba.contracts import (
 )
 from plba.core import ConfigurationManager, RuntimeManager, ServiceContainer
 from plba.health import HealthRegistry
+from plba.http import (
+    ApplicationHttpChannel,
+    ApplicationHttpService,
+    HttpApplicationAppFactory,
+    HttpApplicationChannel,
+    HttpRouteRegistrar,
+    UnifiedHttpService,
+)
 from plba.logging import LogManager
 from plba.queue import InMemoryTaskQueue
 from plba.tracing import MySqlTraceTransport, NoOpTraceTransport, TraceService
@@ -43,7 +51,13 @@ __all__ = [
     "FileConfigProvider",
     "HealthContributor",
     "HealthRegistry",
+    "ApplicationHttpChannel",
+    "ApplicationHttpService",
+    "HttpApplicationAppFactory",
+    "HttpApplicationChannel",
+    "HttpRouteRegistrar",
     "HttpControlChannel",
+    "UnifiedHttpService",
     "InMemoryTaskQueue",
     "LogManager",
     "MySqlTraceTransport",

src/plba/bootstrap.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 from app_runtime.control.http_channel import HttpControlChannel
 from app_runtime.core.runtime import RuntimeManager
 from app_runtime.contracts.application import ApplicationModule
+from app_runtime.http.http_channel import HttpApplicationChannel
 
 
 def create_runtime(
@@ -13,6 +14,9 @@ def create_runtime(
     control_host: str = "127.0.0.1",
     control_port: int = 8080,
     control_timeout: int = 5,
+    application_host: str | None = None,
+    application_port: int = 15000,
+    application_timeout: int = 5,
 ) -> RuntimeManager:
     runtime = RuntimeManager()
     if config_path is not None:
@@ -25,5 +29,13 @@ def create_runtime(
                 timeout=control_timeout,
             )
         )
+    if application_host is not None:
+        runtime.application_http.register_channel(
+            HttpApplicationChannel(
+                host=application_host,
+                port=application_port,
+                timeout=application_timeout,
+            )
+        )
     runtime.register_module(module)
     return runtime

src/plba/http.py

@@ -0,0 +1,14 @@
+from app_runtime.http.base import ApplicationHttpChannel, HttpRouteRegistrar
+from app_runtime.http.http_app import HttpApplicationAppFactory
+from app_runtime.http.http_channel import HttpApplicationChannel
+from app_runtime.http.service import ApplicationHttpService
+from app_runtime.http.unified_service import UnifiedHttpService
+
+__all__ = [
+    "ApplicationHttpChannel",
+    "ApplicationHttpService",
+    "HttpApplicationAppFactory",
+    "HttpApplicationChannel",
+    "HttpRouteRegistrar",
+    "UnifiedHttpService",
+]

tests/test_application_http.py

@@ -0,0 +1,234 @@
+from __future__ import annotations
+
+import http.client
+from dataclasses import dataclass
+from pathlib import Path
+
+from fastapi import FastAPI, File, UploadFile
+from fastapi.responses import FileResponse
+from fastapi.testclient import TestClient
+import pytest
+
+from app_runtime.contracts.application import ApplicationModule
+from app_runtime.control.http_channel import HttpControlChannel
+from app_runtime.core.registration import ModuleRegistry
+from app_runtime.core.runtime import RuntimeManager
+from app_runtime.http.base import ApplicationHttpChannel
+from app_runtime.http.http_channel import HttpApplicationChannel
+from app_runtime.http.unified_service import UnifiedHttpService
+
+try:
+    import python_multipart  # noqa: F401
+except ImportError:
+    HAS_MULTIPART = False
+else:
+    HAS_MULTIPART = True
+
+
+class RecordingChannel(ApplicationHttpChannel):
+    def __init__(self) -> None:
+        self.apps: list[FastAPI] = []
+        self.stop_calls = 0
+
+    async def start(self, app: FastAPI) -> None:
+        self.apps.append(app)
+
+    async def stop(self) -> None:
+        self.stop_calls += 1
+
+
+class PingRoutes:
+    def register(self, app: FastAPI, services) -> None:  # type: ignore[no-untyped-def]
+        @app.get("/estimate/ping")
+        async def ping() -> dict[str, str]:
+            return {"status": "ok"}
+
+
+@dataclass
+class ServiceBackedRoutes:
+    download_path: Path
+
+    def register(self, app: FastAPI, services) -> None:  # type: ignore[no-untyped-def]
+        marker = services.get("task_query_service")
+
+        @app.get("/estimate/api/tasks")
+        async def list_tasks() -> dict[str, object]:
+            return {"marker": marker["marker"]}
+
+        @app.post("/estimate/api/tasks")
+        async def create_task(file: UploadFile = File(...)) -> dict[str, object]:
+            payload = await file.read()
+            return {"filename": file.filename, "size": len(payload)}
+
+        @app.get("/estimate/api/tasks/result")
+        async def download_result() -> FileResponse:
+            return FileResponse(self.download_path, filename=self.download_path.name)
+
+
+class MetricsRoutes:
+    def register(self, app: FastAPI, services) -> None:  # type: ignore[no-untyped-def]
+        @app.get("/estimate/api/metrics")
+        async def metrics() -> dict[str, int]:
+            return {"count": 1}
+
+
+class HttpModule(ApplicationModule):
+    def __init__(self, *registrars: object) -> None:
+        self._registrars = registrars
+
+    @property
+    def name(self) -> str:
+        return "http-module"
+
+    def register(self, registry: ModuleRegistry) -> None:
+        for registrar in self._registrars:
+            registry.add_http_routes(registrar)
+
+
+def _application_client(channel: RecordingChannel) -> TestClient:
+    assert channel.apps
+    return TestClient(channel.apps[0])
+
+
+def _http_request(port: int, path: str) -> tuple[int, bytes]:
+    connection = http.client.HTTPConnection("127.0.0.1", port, timeout=2)
+    try:
+        connection.request("GET", path)
+        response = connection.getresponse()
+        payload = response.read()
+        return response.status, payload
+    finally:
+        connection.close()
+
+
+def test_runtime_starts_application_http_and_registers_routes() -> None:
+    runtime = RuntimeManager()
+    channel = RecordingChannel()
+    runtime.application_http.register_channel(channel)
+    runtime.register_module(HttpModule(PingRoutes()))
+
+    runtime.start(start_control_plane=False)
+    try:
+        assert len(channel.apps) == 1
+        client = _application_client(channel)
+        with client:
+            response = client.get("/estimate/ping")
+            assert response.status_code == 200
+            assert response.json() == {"status": "ok"}
+            assert response.headers["x-response-time-ms"].isdigit()
+    finally:
+        runtime.stop(stop_control_plane=False)
+
+    assert channel.stop_calls == 1
+
+
+def test_application_routes_see_runtime_services_and_support_upload_download(tmp_path: Path) -> None:
+    if not HAS_MULTIPART:
+        pytest.skip("python-multipart is not installed in the local environment")
+
+    runtime = RuntimeManager()
+    runtime.services.register("task_query_service", {"marker": "from-container"})
+    result_path = tmp_path / "result.txt"
+    result_path.write_text("ready", encoding="utf-8")
+
+    channel = RecordingChannel()
+    runtime.application_http.register_channel(channel)
+    runtime.register_module(HttpModule(ServiceBackedRoutes(result_path), MetricsRoutes()))
+    runtime.start(start_control_plane=False)
+    client = _application_client(channel)
+
+    try:
+        with client:
+            list_response = client.get("/estimate/api/tasks")
+            assert list_response.status_code == 200
+            assert list_response.json() == {"marker": "from-container"}
+
+            upload_response = client.post(
+                "/estimate/api/tasks",
+                files={"file": ("input.txt", b"payload", "text/plain")},
+            )
+            assert upload_response.status_code == 200
+            assert upload_response.json() == {"filename": "input.txt", "size": 7}
+
+            metrics_response = client.get("/estimate/api/metrics")
+            assert metrics_response.status_code == 200
+            assert metrics_response.json() == {"count": 1}
+
+            download_response = client.get("/estimate/api/tasks/result")
+            assert download_response.status_code == 200
+            assert download_response.content == b"ready"
+    finally:
+        runtime.stop(stop_control_plane=False)
+
+
+def test_application_http_stop_shuts_down_real_server() -> None:
+    runtime = RuntimeManager()
+    channel = HttpApplicationChannel(host="127.0.0.1", port=0, timeout=2)
+    runtime.application_http.register_channel(channel)
+    runtime.register_module(HttpModule(PingRoutes()))
+    runtime.start(start_control_plane=False)
+
+    try:
+        status, _ = _http_request(channel.port, "/estimate/ping")
+        assert status == 200
+    finally:
+        runtime.stop(stop_control_plane=False)
+
+    try:
+        _http_request(channel.port, "/estimate/ping")
+    except OSError:
+        pass
+    else:
+        raise AssertionError("application HTTP server is still reachable after stop")
+
+
+def test_control_plane_and_application_http_work_independently() -> None:
+    runtime = RuntimeManager()
+    control_channel = HttpControlChannel(host="127.0.0.1", port=0, timeout=2)
+    app_channel = HttpApplicationChannel(host="127.0.0.1", port=0, timeout=2)
+    runtime.control_plane.register_channel(control_channel)
+    runtime.application_http.register_channel(app_channel)
+    runtime.register_module(HttpModule(PingRoutes()))
+    runtime.start()
+
+    try:
+        control_status, _ = _http_request(control_channel.port, "/health")
+        app_status, _ = _http_request(app_channel.port, "/estimate/ping")
+        assert control_status == 200
+        assert app_status == 200
+
+        control_missing_status, _ = _http_request(control_channel.port, "/estimate/ping")
+        app_missing_status, _ = _http_request(app_channel.port, "/health")
+        assert control_missing_status == 404
+        assert app_missing_status == 404
+
+        runtime.application_http.stop()
+        control_status, _ = _http_request(control_channel.port, "/health")
+        assert control_status == 200
+    finally:
+        runtime.control_plane.stop()
+        runtime.stop(stop_control_plane=False)
+
+
+def test_unified_http_serves_control_and_application_routes_on_one_app() -> None:
+    runtime = RuntimeManager(application_http=UnifiedHttpService())
+    channel = RecordingChannel()
+    runtime.application_http.register_channel(channel)
+    runtime.register_module(HttpModule(PingRoutes()))
+    runtime.start(start_control_plane=False)
+
+    try:
+        client = _application_client(channel)
+        with client:
+            health_response = client.get("/health")
+            action_response = client.get("/actions/status")
+            app_response = client.get("/estimate/ping")
+
+            assert health_response.status_code == 200
+            assert health_response.json()["status"] == "ok"
+            assert action_response.status_code == 200
+            assert action_response.json() == {"status": "ok", "detail": "idle"}
+            assert app_response.status_code == 200
+            assert app_response.json() == {"status": "ok"}
+    finally:
+        runtime.stop(stop_control_plane=False)

tests/test_trace_endpoint.py

@@ -46,7 +46,7 @@ def _build_client(trace_provider=None) -> TestClient:
     return TestClient(app)
 
 
-def test_trace_endpoint_returns_text_with_default_levels() -> None:
+def test_trace_endpoint_returns_html_by_default() -> None:
     captured: list[tuple[str, TraceQueryRequest]] = []
 
     async def trace_provider(trace_id: str, request: TraceQueryRequest) -> TraceLogView:
@@ -67,6 +67,42 @@ def test_trace_endpoint_returns_text_with_default_levels() -> None:
     finally:
         client.close()
 
+    assert response.status_code == 200
+    assert response.headers["content-type"].startswith("text/html")
+    assert "trace_id:" in response.text
+    assert "first error" in response.text
+    assert "second warning" in response.text
+    assert captured == [
+        (
+            "trace-1",
+            TraceQueryRequest(
+                levels=("ERROR", "WARNING", "INFO"),
+                include_attrs_json=False,
+                response_format="html",
+                ancestor_depth=0,
+            ),
+        )
+    ]
+
+
+def test_trace_endpoint_returns_text_when_requested() -> None:
+    async def trace_provider(_trace_id: str, _request: TraceQueryRequest) -> TraceLogView:
+        return TraceLogView(
+            trace_id="trace-1",
+            parent_id="root-trace",
+            child_ids=("child-1", "child-2"),
+            records=(
+                _trace_record(row_id=1, level="ERROR", message="first error"),
+                _trace_record(row_id=2, level="WARNING", message="second warning"),
+            ),
+        )
+
+    client = _build_client(trace_provider)
+    try:
+        response = client.get("/traces/trace-1?format=text")
+    finally:
+        client.close()
+
     assert response.status_code == 200
     assert response.text == (
         "trace_id: trace-1\n"
@@ -74,12 +110,14 @@ def test_trace_endpoint_returns_text_with_default_levels() -> None:
         "child_ids:\n"
         " - child-1\n"
         " - child-2\n"
-        "--------------------------------------------------\n"
+        "\n"
+        "==============================\n"
+        "trace_id: trace-1\n"
+        "\n"
         "step: process\n"
         "first error\n"
         "second warning"
     )
-    assert captured == [("trace-1", TraceQueryRequest(levels=("ERROR", "WARNING", "INFO"), include_attrs_json=False, response_format="text"))]
 
 
 def test_trace_endpoint_appends_attrs_json_in_text_mode() -> None:
@@ -95,7 +133,7 @@ def test_trace_endpoint_appends_attrs_json_in_text_mode() -> None:
 
     client = _build_client(trace_provider)
     try:
-        response = client.get("/traces/trace-1?attrs_json=true")
+        response = client.get("/traces/trace-1?format=text&attrs_json=true")
     finally:
         client.close()
 
@@ -104,7 +142,10 @@ def test_trace_endpoint_appends_attrs_json_in_text_mode() -> None:
         "trace_id: trace-1\n"
         "parent_id: \n"
         "child_ids:\n"
-        "--------------------------------------------------\n"
+        "\n"
+        "==============================\n"
+        "trace_id: trace-1\n"
+        "\n"
         "step: process\n"
         'failure, {"attempt":2,"source":"crm"}'
     )
@@ -125,7 +166,7 @@ def test_trace_endpoint_separates_messages_by_step_in_text_mode() -> None:
 
     client = _build_client(trace_provider)
     try:
-        response = client.get("/traces/trace-1")
+        response = client.get("/traces/trace-1?format=text")
     finally:
         client.close()
 
@@ -134,11 +175,14 @@ def test_trace_endpoint_separates_messages_by_step_in_text_mode() -> None:
         "trace_id: trace-1\n"
         "parent_id: \n"
         "child_ids:\n"
-        "--------------------------------------------------\n"
+        "\n"
+        "==============================\n"
+        "trace_id: trace-1\n"
+        "\n"
         "step: load_stocks\n"
         "load first\n"
         "load second\n"
-        "--------------------------------------------------\n"
+        "------------------------------\n"
         "step: filter_stocks\n"
         "filter first"
     )
@@ -178,14 +222,229 @@ def test_trace_endpoint_returns_json_payload() -> None:
                 "attrs_json": {"batch": 7},
             }
         ],
+        "ancestors": [],
     }
 
 
+def test_trace_endpoint_returns_json_payload_with_ancestors() -> None:
+    async def trace_provider(_trace_id: str, _request: TraceQueryRequest) -> TraceLogView:
+        return TraceLogView(
+            trace_id="trace-1",
+            parent_id="parent-1",
+            child_ids=("child-1",),
+            records=(
+                _trace_record(row_id=3, level="INFO", message="done", attrs_json={"batch": 7}),
+            ),
+            ancestors=(
+                TraceLogView(
+                    trace_id="root-1",
+                    parent_id=None,
+                    child_ids=("parent-1",),
+                    records=(
+                        _trace_record(row_id=4, level="INFO", message="root info"),
+                    ),
+                ),
+                TraceLogView(
+                    trace_id="parent-1",
+                    parent_id="root-1",
+                    child_ids=("trace-1", "sibling-1"),
+                    records=(
+                        _trace_record(row_id=5, level="WARNING", message="parent warning"),
+                    ),
+                ),
+            ),
+        )
+
+    client = _build_client(trace_provider)
+    try:
+        response = client.get("/traces/trace-1?format=json&ancestor_depth=1")
+    finally:
+        client.close()
+
+    assert response.status_code == 200
+    assert response.json()["ancestors"] == [
+        {
+            "trace_id": "root-1",
+            "parent_id": "",
+            "child_ids": ["parent-1"],
+            "messages": [
+                {
+                    "id": 4,
+                    "trace_id": "trace-1",
+                    "event_time": "2026-04-28T10:11:12+00:00",
+                    "step": "process",
+                    "status": "failed",
+                    "level": "INFO",
+                    "message": "root info",
+                }
+            ],
+        },
+        {
+            "trace_id": "parent-1",
+            "parent_id": "root-1",
+            "child_ids": ["trace-1", "sibling-1"],
+            "messages": [
+                {
+                    "id": 5,
+                    "trace_id": "trace-1",
+                    "event_time": "2026-04-28T10:11:12+00:00",
+                    "step": "process",
+                    "status": "failed",
+                    "level": "WARNING",
+                    "message": "parent warning",
+                }
+            ],
+        }
+    ]
+
+
+def test_trace_endpoint_returns_html_page_with_related_links() -> None:
+    async def trace_provider(_trace_id: str, _request: TraceQueryRequest) -> TraceLogView:
+        return TraceLogView(
+            trace_id="trace-1",
+            parent_id="parent-1",
+            child_ids=("child-1", "child-2"),
+            records=(
+                _trace_record(row_id=1, level="INFO", message="loaded prices", step="load_stocks", status="ok"),
+                _trace_record(row_id=2, level="WARNING", message="filtered suspicious ticker", step="filter_stocks", status="degraded"),
+            ),
+        )
+
+    client = _build_client(trace_provider)
+    try:
+        response = client.get("/traces/trace-1?format=html&attrs_json=true")
+    finally:
+        client.close()
+
+    assert response.status_code == 200
+    assert response.headers["content-type"].startswith("text/html")
+    assert "background: var(--bg);" in response.text
+    assert "--bg: #000000;" in response.text
+    assert "--fg: #ececec;" in response.text
+    assert "--step: #ffffff;" in response.text
+    assert "--info: #d6d7d9;" in response.text
+    assert "--warning: #e9ebec;" in response.text
+    assert "--error: #ff817d;" in response.text
+    assert "--other: #ececec;" in response.text
+    assert 'font: 13px/1.1 "SFMono-Regular", monospace;' in response.text
+    assert '<div class="line">trace_id: <a href="/traces/trace-1?format=html&amp;levels=ERROR%2CWARNING%2CINFO&amp;attrs_json=true">trace-1</a></div>' in response.text
+    assert '<div class="line">parent_id: <a href="/traces/parent-1?format=html&amp;levels=ERROR%2CWARNING%2CINFO&amp;attrs_json=true">parent-1</a></div>' in response.text
+    assert '<div class="line">child_ids:</div>' in response.text
+    assert '<div class="line"> - <a href="/traces/child-1?format=html&amp;levels=ERROR%2CWARNING%2CINFO&amp;attrs_json=true">child-1</a></div>' in response.text
+    assert '<div class="line"> - <a href="/traces/child-2?format=html&amp;levels=ERROR%2CWARNING%2CINFO&amp;attrs_json=true">child-2</a></div>' in response.text
+    assert '<div class="line">==============================</div>' in response.text
+    assert '<div class="line" style="color: var(--step);">load_stocks</div>' in response.text
+    assert '<div class="line">trace_id: <a href="/traces/trace-1?format=html&amp;levels=ERROR%2CWARNING%2CINFO&amp;attrs_json=true">trace-1</a></div>' in response.text
+    assert '<div class="line" style="color: var(--step);">filter_stocks</div>' in response.text
+    assert "loaded prices" in response.text
+    assert "filtered suspicious ticker" in response.text
+    assert "2026-04-28T10:11:12+00:00 | INFO | ok" not in response.text
+    assert "2026-04-28T10:11:12+00:00 | WARNING | degraded" not in response.text
+    assert "Related Traces" not in response.text
+
+
+def test_trace_endpoint_renders_ancestors_in_text_mode() -> None:
+    async def trace_provider(_trace_id: str, _request: TraceQueryRequest) -> TraceLogView:
+        return TraceLogView(
+            trace_id="trace-1",
+            parent_id="parent-1",
+            child_ids=(),
+            records=(_trace_record(row_id=1, level="INFO", message="child message"),),
+            ancestors=(
+                TraceLogView(
+                    trace_id="root-1",
+                    parent_id=None,
+                    child_ids=("parent-1",),
+                    records=(_trace_record(row_id=2, level="INFO", message="root message"),),
+                ),
+                TraceLogView(
+                    trace_id="parent-1",
+                    parent_id="root-1",
+                    child_ids=("trace-1",),
+                    records=(_trace_record(row_id=3, level="WARNING", message="parent message"),),
+                ),
+            ),
+        )
+
+    client = _build_client(trace_provider)
+    try:
+        response = client.get("/traces/trace-1?format=text&ancestor_depth=1")
+    finally:
+        client.close()
+
+    assert response.status_code == 200
+    assert response.text == (
+        "trace_id: trace-1\n"
+        "parent_id: parent-1\n"
+        "child_ids:\n"
+        "\n"
+        "==============================\n"
+        "trace_id: root-1\n"
+        "\n"
+        "step: process\n"
+        "root message\n"
+        "\n"
+        "\n"
+        "==============================\n"
+        "trace_id: parent-1\n"
+        "\n"
+        "step: process\n"
+        "parent message\n"
+        "\n"
+        "\n"
+        "==============================\n"
+        "trace_id: trace-1\n"
+        "\n"
+        "step: process\n"
+        "child message"
+    )
+
+
+def test_trace_endpoint_preserves_ancestor_depth_in_html_links() -> None:
+    async def trace_provider(_trace_id: str, _request: TraceQueryRequest) -> TraceLogView:
+        return TraceLogView(
+            trace_id="trace-1",
+            parent_id="parent-1",
+            child_ids=("child-1",),
+            records=(_trace_record(row_id=1, level="INFO", message="loaded prices"),),
+            ancestors=(
+                TraceLogView(
+                    trace_id="root-1",
+                    parent_id=None,
+                    child_ids=("parent-1",),
+                    records=(_trace_record(row_id=2, level="INFO", message="root info"),),
+                ),
+                TraceLogView(
+                    trace_id="parent-1",
+                    parent_id="root-1",
+                    child_ids=("trace-1",),
+                    records=(_trace_record(row_id=3, level="WARNING", message="parent warning"),),
+                ),
+            ),
+        )
+
+    client = _build_client(trace_provider)
+    try:
+        response = client.get("/traces/trace-1?format=html&attrs_json=true&ancestor_depth=all")
+    finally:
+        client.close()
+
+    assert response.status_code == 200
+    assert 'href="/traces/trace-1?format=html&amp;levels=ERROR%2CWARNING%2CINFO&amp;attrs_json=true&amp;ancestor_depth=all"' in response.text
+    assert 'href="/traces/root-1?format=html&amp;levels=ERROR%2CWARNING%2CINFO&amp;attrs_json=true&amp;ancestor_depth=all"' in response.text
+    assert 'href="/traces/parent-1?format=html&amp;levels=ERROR%2CWARNING%2CINFO&amp;attrs_json=true&amp;ancestor_depth=all"' in response.text
+    assert response.text.index("root info") < response.text.index("parent warning") < response.text.index("loaded prices")
+    assert "root info" in response.text
+    assert "parent warning" in response.text
+
+
 def test_trace_endpoint_validates_query_params() -> None:
     client = _build_client(lambda _trace_id, _request: None)
     try:
         invalid_level = client.get("/traces/trace-1?levels=error,fatal")
         invalid_format = client.get("/traces/trace-1?format=xml")
+        invalid_ancestor_depth = client.get("/traces/trace-1?ancestor_depth=-1")
+        invalid_ancestor_type = client.get("/traces/trace-1?ancestor_depth=up")
     finally:
         client.close()
 
@@ -193,6 +452,16 @@ def test_trace_endpoint_validates_query_params() -> None:
     assert invalid_level.json() == {"status": "error", "detail": "unsupported trace levels: FATAL"}
     assert invalid_format.status_code == 400
     assert invalid_format.json() == {"status": "error", "detail": "unsupported trace format: xml"}
+    assert invalid_ancestor_depth.status_code == 400
+    assert invalid_ancestor_depth.json() == {
+        "status": "error",
+        "detail": "query parameter must be >= 0: ancestor_depth=-1",
+    }
+    assert invalid_ancestor_type.status_code == 400
+    assert invalid_ancestor_type.json() == {
+        "status": "error",
+        "detail": "invalid ancestor depth query parameter: ancestor_depth=up",
+    }
 
 
 def test_runtime_trace_logs_uses_configured_reader(monkeypatch) -> None:
@@ -204,15 +473,21 @@ def test_runtime_trace_logs_uses_configured_reader(monkeypatch) -> None:
     )
 
     class StubReader:
-        def read_trace(self, trace_id: str, levels: tuple[str, ...]) -> TraceLogView | None:
+        def read_trace(
+            self,
+            trace_id: str,
+            levels: tuple[str, ...],
+            ancestor_depth: int | None = 0,
+        ) -> TraceLogView | None:
             assert trace_id == "trace-1"
             assert levels == ("ERROR",)
+            assert ancestor_depth is None
             return expected
 
     monkeypatch.setattr(runtime_module, "build_trace_log_reader", lambda _transport: StubReader())
     runtime = RuntimeManager()
 
-    result = asyncio.run(runtime.trace_logs("trace-1", TraceQueryRequest(levels=("ERROR",))))
+    result = asyncio.run(runtime.trace_logs("trace-1", TraceQueryRequest(levels=("ERROR",), ancestor_depth=None)))
 
     assert result == expected
 
@@ -228,7 +503,11 @@ def test_mysql_trace_log_reader_maps_db_rows() -> None:
             self._current_query = query
 
         def fetchone(self) -> dict[str, object] | None:
-            return {"parent_id": "root-77"}
+            if self.executed[-1][1] == ("trace-1",):
+                return {"parent_id": "root-77"}
+            if self.executed[-1][1] == ("root-77",):
+                return {"parent_id": None}
+            return None
 
         def fetchall(self) -> list[dict[str, object]]:
             if "WHERE parent_id = %s" in self._current_query:
@@ -293,7 +572,167 @@ def test_mysql_trace_log_reader_maps_db_rows() -> None:
                 attrs_json={"attempt": 1},
             ),
         ),
+        ancestors=(),
     )
     assert len(factory.cursor.executed) == 3
     assert factory.cursor.executed[1][1] == ("trace-1",)
     assert factory.cursor.executed[2][1] == ("trace-1", "ERROR", "WARNING")
+
+
+def test_mysql_trace_log_reader_loads_requested_ancestors() -> None:
+    class FakeCursor:
+        def __init__(self) -> None:
+            self.executed: list[tuple[str, tuple[object, ...]]] = []
+            self._current_query = ""
+
+        def execute(self, query: str, params: tuple[object, ...]) -> None:
+            self.executed.append((query, params))
+            self._current_query = query
+
+        def fetchone(self) -> dict[str, object] | None:
+            if self.executed[-1][1] == ("trace-1",):
+                return {"parent_id": "parent-1"}
+            if self.executed[-1][1] == ("parent-1",):
+                return {"parent_id": "root-1"}
+            if self.executed[-1][1] == ("root-1",):
+                return {"parent_id": None}
+            return None
+
+        def fetchall(self) -> list[dict[str, object]]:
+            if "WHERE parent_id = %s" in self._current_query:
+                parent_id = self.executed[-1][1][0]
+                if parent_id == "trace-1":
+                    return []
+                if parent_id == "parent-1":
+                    return [{"trace_id": "trace-1"}]
+                if parent_id == "root-1":
+                    return [{"trace_id": "parent-1"}]
+                return []
+            trace_id = self.executed[-1][1][0]
+            return [
+                {
+                    "id": 8 if trace_id == "trace-1" else 9,
+                    "trace_id": trace_id,
+                    "event_time": datetime(2026, 4, 28, 10, 11, 12, tzinfo=timezone.utc),
+                    "step": "parse",
+                    "status": "failed",
+                    "level": "ERROR",
+                    "message": f"broken:{trace_id}",
+                    "attrs_json": '{"attempt":1}',
+                }
+            ]
+
+        def __enter__(self) -> FakeCursor:
+            return self
+
+        def __exit__(self, exc_type, exc, tb) -> None:
+            return None
+
+    class FakeConnection:
+        def __init__(self, cursor: FakeCursor) -> None:
+            self._cursor = cursor
+
+        def cursor(self) -> FakeCursor:
+            return self._cursor
+
+        def __enter__(self) -> FakeConnection:
+            return self
+
+        def __exit__(self, exc_type, exc, tb) -> None:
+            return None
+
+    class FakeConnectionFactory:
+        def __init__(self) -> None:
+            self.cursor = FakeCursor()
+
+        def connect(self) -> FakeConnection:
+            return FakeConnection(self.cursor)
+
+    factory = FakeConnectionFactory()
+    reader = MySqlTraceLogReader(factory)  # type: ignore[arg-type]
+
+    view = reader.read_trace("trace-1", ("ERROR",), 1)
+
+    assert view is not None
+    assert view.trace_id == "trace-1"
+    assert view.parent_id == "parent-1"
+    assert len(view.ancestors) == 1
+    assert view.ancestors[0].trace_id == "parent-1"
+    assert view.ancestors[0].parent_id == "root-1"
+    assert view.ancestors[0].child_ids == ("trace-1",)
+
+
+def test_mysql_trace_log_reader_orders_ancestors_root_first() -> None:
+    class FakeCursor:
+        def __init__(self) -> None:
+            self.executed: list[tuple[str, tuple[object, ...]]] = []
+            self._current_query = ""
+
+        def execute(self, query: str, params: tuple[object, ...]) -> None:
+            self.executed.append((query, params))
+            self._current_query = query
+
+        def fetchone(self) -> dict[str, object] | None:
+            if self.executed[-1][1] == ("trace-1",):
+                return {"parent_id": "parent-1"}
+            if self.executed[-1][1] == ("parent-1",):
+                return {"parent_id": "root-1"}
+            if self.executed[-1][1] == ("root-1",):
+                return {"parent_id": None}
+            return None
+
+        def fetchall(self) -> list[dict[str, object]]:
+            if "WHERE parent_id = %s" in self._current_query:
+                parent_id = self.executed[-1][1][0]
+                if parent_id == "root-1":
+                    return [{"trace_id": "parent-1"}]
+                if parent_id == "parent-1":
+                    return [{"trace_id": "trace-1"}]
+                return []
+            trace_id = self.executed[-1][1][0]
+            return [
+                {
+                    "id": 8,
+                    "trace_id": trace_id,
+                    "event_time": datetime(2026, 4, 28, 10, 11, 12, tzinfo=timezone.utc),
+                    "step": "parse",
+                    "status": "failed",
+                    "level": "ERROR",
+                    "message": f"broken:{trace_id}",
+                    "attrs_json": '{"attempt":1}',
+                }
+            ]
+
+        def __enter__(self) -> FakeCursor:
+            return self
+
+        def __exit__(self, exc_type, exc, tb) -> None:
+            return None
+
+    class FakeConnection:
+        def __init__(self, cursor: FakeCursor) -> None:
+            self._cursor = cursor
+
+        def cursor(self) -> FakeCursor:
+            return self._cursor
+
+        def __enter__(self) -> FakeConnection:
+            return self
+
+        def __exit__(self, exc_type, exc, tb) -> None:
+            return None
+
+    class FakeConnectionFactory:
+        def __init__(self) -> None:
+            self.cursor = FakeCursor()
+
+        def connect(self) -> FakeConnection:
+            return FakeConnection(self.cursor)
+
+    factory = FakeConnectionFactory()
+    reader = MySqlTraceLogReader(factory)  # type: ignore[arg-type]
+
+    view = reader.read_trace("trace-1", ("ERROR",), 2)
+
+    assert view is not None
+    assert tuple(ancestor.trace_id for ancestor in view.ancestors) == ("root-1", "parent-1")