feat(cherry-pick): fixes for 0.3.1 release (#3998)

## Summary

Cherry-picks 5 critical fixes from main to the release-0.3.x branch for
the v0.3.1 release, plus CI workflow updates.

**Note**: This recreates the cherry-picks from the closed PR #3991, now
targeting the renamed `release-0.3.x` branch (previously
`release-0.3.x-maint`).

## Commits

1. **2c56a8560** - fix(context): prevent provider data leak between
streaming requests (#3924)
- **CRITICAL SECURITY FIX**: Prevents provider credentials from leaking
between requests
   - Fixed import path for 0.3.0 compatibility

2. **ddd32b187** - fix(inference): enable routing of models with
provider_data alone (#3928)
   - Enables routing for fully qualified model IDs with provider_data
   - Resolved merge conflicts, adapted for 0.3.0 structure

3. **f7c2973aa** - fix: Avoid BadRequestError due to invalid max_tokens
(#3667)
- Fixes failures with Gemini and other providers that reject
max_tokens=0
   - Non-breaking API change

4. **d7f9da616** - fix(responses): sync conversation before yielding
terminal events in streaming (#3888)
- Ensures conversation sync executes even when streaming consumers break
early

5. **0ffa8658b** - fix(logging): ensure logs go to stderr, loggers obey
levels (#3885)
   - Fixes logging infrastructure

6. **75b49cb3c** - ci: support release branches and match client branch
(#3990)
   - Updates CI workflows to support release-X.Y.x branches
- Matches client branch from llama-stack-client-python for release
testing
   - Fixes artifact name collisions

## Adaptations for 0.3.0

- Fixed import paths: `llama_stack.core.telemetry.tracing` →
`llama_stack.providers.utils.telemetry.tracing`
- Fixed import paths: `llama_stack.core.telemetry.telemetry` →
`llama_stack.apis.telemetry`
- Changed `self.telemetry_enabled` → `self.telemetry` (0.3.0 attribute
name)
- Removed `rerank()` method that doesn't exist in 0.3.0

## Testing

All imports verified and tests should pass once CI is set up.

llama_stack/core/utils/context.py

@@ -7,6 +7,10 @@
 from collections.abc import AsyncGenerator
 from contextvars import ContextVar
 
+from llama_stack.providers.utils.telemetry.tracing import CURRENT_TRACE_CONTEXT
+
+_MISSING = object()
+
 
 def preserve_contexts_async_generator[T](
     gen: AsyncGenerator[T, None], context_vars: list[ContextVar]
@@ -21,20 +25,60 @@ def preserve_contexts_async_generator[T](
 
     async def wrapper() -> AsyncGenerator[T, None]:
         while True:
+            previous_values: dict[ContextVar, object] = {}
+            tokens: dict[ContextVar, object] = {}
+
+            # Restore ALL context values before any await and capture previous state
+            # This is needed to propagate context across async generator boundaries
+            for context_var in context_vars:
+                try:
+                    previous_values[context_var] = context_var.get()
+                except LookupError:
+                    previous_values[context_var] = _MISSING
+                tokens[context_var] = context_var.set(initial_context_values[context_var.name])
+
+            def _restore_context_var(context_var: ContextVar, *, _tokens=tokens, _prev=previous_values) -> None:
+                token = _tokens.get(context_var)
+                previous_value = _prev.get(context_var, _MISSING)
+                if token is not None:
+                    try:
+                        context_var.reset(token)
+                        return
+                    except (RuntimeError, ValueError):
+                        pass
+
+                if previous_value is _MISSING:
+                    context_var.set(None)
+                else:
+                    context_var.set(previous_value)
+
             try:
-                # Restore context values before any await
-                for context_var in context_vars:
-                    context_var.set(initial_context_values[context_var.name])
-
                 item = await gen.__anext__()
-
-                # Update our tracked values with any changes made during this iteration
-                for context_var in context_vars:
-                    initial_context_values[context_var.name] = context_var.get()
-
-                yield item
-
             except StopAsyncIteration:
+                # Restore all context vars before exiting to prevent leaks
+                # Use _restore_context_var for all vars to properly restore to previous values
+                for context_var in context_vars:
+                    _restore_context_var(context_var)
                 break
+            except Exception:
+                # Restore all context vars on exception
+                for context_var in context_vars:
+                    _restore_context_var(context_var)
+                raise
+
+            try:
+                yield item
+                # Update our tracked values with any changes made during this iteration
+                # Only for non-trace context vars - trace context must persist across yields
+                # to allow nested span tracking for telemetry
+                for context_var in context_vars:
+                    if context_var is not CURRENT_TRACE_CONTEXT:
+                        initial_context_values[context_var.name] = context_var.get()
+            finally:
+                # Restore non-trace context vars after each yield to prevent leaks between requests
+                # CURRENT_TRACE_CONTEXT is NOT restored here to preserve telemetry span stack
+                for context_var in context_vars:
+                    if context_var is not CURRENT_TRACE_CONTEXT:
+                        _restore_context_var(context_var)
 
     return wrapper()