Fix incoming: scope["route"].path loses include_router() prefixes #16177

Summary

Fix a regression introduced in FastAPI 0.137.0 where HTTP routes added with include_router() lose their include-time prefixes in request.scope["route"].path and request.scope["route"].path_format.

For example, a route registered as:

/users/{user_id}

and included with:

prefix="/api"

should expose:

/api/users/{user_id}

but currently exposes:

/users/{user_id}.

This regression was reported in Discussion #16051.

Why this matters

scope["route"] is commonly used by middleware and instrumentation for logging, tracing, and metrics.

When included routes lose their prefixes, distinct endpoints such as:

• /users/{id}
• /orders/{id}

can be incorrectly represented by the same route label.

Root cause

Three routing paths were still writing the original, unprefixed APIRoute into scope["route"] even when an effective include-time route context was available:

• APIRoute.matches()
• _IncludedRouter._handle_selected()
• APIRouter.app() low-priority route handling

The effective prefixed path already exists in RouteContext / _EffectiveRouteContext, but it was not being exposed through scope["route"].

Fix

Use the existing RouteContext facade when an effective route context applies.

This allows scope["route"] to expose the effective .path and .path_format while preserving access to the underlying route through .original_route.

Tests

Added focused regression tests covering:

• include_router() with a prefix
• nested router prefixes
• HTTP/WebSocket parity
• middleware-observed scope["route"]

The new tests fail without the fix and pass with it.

Full test suite:

• 3328 passed
• 19 skipped
• 5 xfailed
• 0 failed

Related discussion

This PR addresses the regression reported in #16051.

Notes

For included HTTP routes, scope["route"] now exposes a RouteContext instead of the original APIRoute. Attribute access such as .path, .path_format, .name, and .endpoint continues to work, while .original_route provides access to the underlying route object.

PR: #16176