Fix V1 chat page HTTP 500 from missing reasoning resolver import

[Paul Lizer (paullizer)]

Summary

• Restore the explicit reasoning-policy resolver import used by V1's initial model selector. A catalog refactor removed the import but retained the call, causing authenticated /chats startup to raise NameError with nonempty model catalogs.
• Add fresh-process, real-web regression coverage for legacy, APIM, and multi-endpoint catalogs, warm/cold startup, preferences, reasoning metadata, and access controls. Preserve existing model-selection behavior and V2 routes; document the fix in version 0.261.327.

Linked issue

N/A. The user requested investigation and implementation without creating an issue.

Release Notes & Latest Features

• New Feature
• Bug Fix
• UI Enhancement
• Breaking Change
• Internal only

Is this visible to end users?

• Yes
• No

Is this admin-facing (Admin Settings, governance, deployment, config)?

• Yes
• No

Should this become a Latest Feature card?

• Yes
• No
• Already added

Screenshot needed for the card?

• Yes
• No
• Attached

Version bump

• application/single_app/config.py VERSION third segment bumped, or not needed because this is docs-only
• deployers/version.txt bumped, or not needed because deployers/ was not changed

Application version: 0.261.326 -> 0.261.327. No deployer changes.

Testing / validation

• python -m pytest -q .\functional_tests\test_chat_v1_page_bootstrap.py before the fix: 4 failed as expected, including the actual authenticated route's missing-resolver exception in normal/optimized Python.
• python -m pytest -q .\functional_tests\test_chat_v1_page_bootstrap.py .\functional_tests\test_chat_model_selector_initial_multiendpoint_bootstrap.py: 7 passed, including the final run after the version bump.
• python -m pytest -q .\functional_tests\test_model_reasoning_capability_resolution.py .\functional_tests\test_chat_retry_import_boundaries.py: 31 passed, plus 64 passing subtests.
• python -m pytest -q .\functional_tests\test_v2_ui_spa_route.py: 6 passed.
• python .\functional_tests\route_tests\test_route_blueprint_policy_inventory.py: 15 passed.
• python .\functional_tests\route_tests\test_route_unauthenticated_policy_contract.py: 10 passed.
• python .\functional_tests\route_tests\test_route_policy_test_coverage.py: 3 passed.
• python .\functional_tests\test_docs_app_surface_coverage.py: 7 passed; inventory remains current.
• python .\functional_tests\test_docs_site_quality.py: 6 passed.
• python -m pytest -q .\ui_tests\test_chat_page_multi_endpoint_notice_render.py .\ui_tests\test_staging_chat_smoke.py: 2 skipped because no authenticated deployed environment was configured.
• git -c core.whitespace=blank-at-eol,blank-at-eof,space-before-tab,cr-at-eol diff --check: passed.

Application integration tests used a session-local virtual environment with repository Flask/Werkzeug/Semantic Kernel versions and compatible TLS dependencies to resolve the default interpreter's unrelated OpenSSL import failure. Shared interpreter packages and dependency manifests are unchanged.

The deployed screenshot did not include a server traceback. This defect was reproduced through the real local route, but deployed page loading and a complete model send/response cycle remain unverified. An unrelated existing bootstrap-safety test still expects the previously removed migration notice; it remains unchanged and is documented in the fix notes.

Documentation

• Release notes updated, or not needed
• Feature documentation updated, or not needed
• Fix documentation updated, or not needed

Added docs/explanation/fixes/V1_CHAT_PAGE_BOOTSTRAP_FIX.md. Release notes remain unchanged pending user approval. No new feature surface is introduced.

Security checklist

• New Flask routes include @swagger_route(security=get_auth_security())
• Settings sent to non-admin frontends use sanitize_settings_for_user()
• Browser JavaScript is served from local SimpleChat static assets only; no CDN-hosted JS
• No secrets, keys, connection strings, or local-only artifacts are included

No new routes or browser assets. Runtime tests retain actual authentication decorators and sanitizer, and check that synthetic credential/private endpoint markers are absent from rendered HTML.