refactor(bridge): remove _validation_contract read mirror after deprecation cycle

[yeongseon]

Context

Part of umbrella yeongseon/azure-functions-validation-python#270. Once the endpoint namespace is the primary path and producers have shipped it for a deprecation cycle, the read-side mirror _validation_contract.py and the validation-reconstruction logic in bridge.py can be removed. Do not rush — only after the fallback has lived through at least one minor release.

Acceptance Checklist

• Confirm all in-toolkit producers emit endpoint for >= 1 minor release.
• Remove _validation_contract.py and the validation-only reconstruction code paths.
• Keep or migrate any still-needed constants.
• Update tests to drop the fallback-only cases.
• Note the removal in CHANGELOG.

Out of scope

• Landing the endpoint reader + fallback (prerequisite issue).

References

• Umbrella: feat(metadata): converge cross-package endpoint metadata without new foundation packages azure-functions-validation-python#270

[yeongseon]

Deferred — deprecation gate not yet met.

The endpoint-namespace reader + validation fallback (#311 / #314) is currently unreleased: it was merged on 2026-08-07, after the latest tag v0.19.1 (2026-07-18), and is not part of any published minor. The acceptance checklist here requires the fallback to have "lived through at least one minor release" before the _validation_contract.py read mirror is removed.

Action: Keep this issue open and blocked until:

1. A minor release ships the endpoint reader + fallback (e.g. v0.20.0), and
2. All in-toolkit producers have emitted endpoint for >= 1 minor release.

No code change is due yet. Revisit after the next minor release.

[yeongseon]

Deprecation-gate status check (not yet ready)

Investigated the deprecation gate before acting. Convergence is complete, but the deprecation period has not elapsed — deferring.

Evidence

Item	State
Umbrella azure-functions-validation-python#270	✅ CLOSED — all producers emit endpoint
Cookbook published-version E2E (azure-functions-cookbook-python#119)	✅ CLOSED — endpoint-driven spec verified identical
validation producer (endpoint in _make_wrapper, #275)	first shipped in validation v0.9.0 (current: v0.9.1)
openapi endpoint reader + validation fallback (#314, 38e8a48)	contained only in v0.20.0 (the current release)

Why not now

This issue's own gate: "only after the fallback has lived through at least one minor release". The openapi read-side fallback shipped in v0.20.0, which is the current release — zero minor releases have elapsed since. Umbrella #270 also explicitly classifies this as post-convergence cleanup gated on a deprecation period, not part of convergence.

Re-evaluation trigger

Revisit once openapi has shipped >= v0.21.0 (i.e. at least one minor release after v0.20.0) with the endpoint reader live. At that point:

• Confirm no in-toolkit producer regressed to validation-only emission.
• Remove src/azure_functions_openapi/_validation_contract.py + the validation-reconstruction paths in bridge.py (_read_validation_hints, namespace-fallback skew).
• Drop fallback-only tests; keep endpoint-path coverage.
• Note the removal in CHANGELOG.

Keeping this issue open and deferred — no code change made in this pass.

[yeongseon]

Deprecation-cycle gate check — not yet ready

Verified the preconditions before removing the _validation_contract read mirror:

Producer side (satisfied):

• azure-functions-validation emits the endpoint namespace since v0.9.0 (currently 0.10.1), and still writes both endpoint + legacy validation namespaces (decorator.py, _endpoint.py:set_endpoint_metadata). So producers have emitted endpoint for ≥1 minor release. ✅
• azure-functions-langgraph emits endpoint (docs: merge redundant Features list into What it does #294). durable-graph is self-contained by design (does not emit). ✅

Consumer deprecation-cycle gate (NOT satisfied):

• The endpoint reader + validation fallback landed in openapi 0.21.0 (feat(bridge): read endpoint namespace, prefer over validation with fallback #311, released 2026-08-11). The current release is 0.21.1 — a patch on the same minor. The issue's guard is explicit: "Do not rush — only after the fallback has lived through at least one minor release." No 0.22.x minor has shipped since the fallback was introduced. ❌
• Umbrella chore(deps): bump mypy from 2.1.0 to 2.3.0 #270's convergence close condition (cookbook chore: release v0.15.0 #119, published-version E2E) is also still open; refactor(bridge): remove _validation_contract read mirror after deprecation cycle #313 is post-convergence cleanup gated on that deprecation period.

Conclusion: Deferring removal until the fallback has shipped through at least one subsequent minor release (≥ 0.22.0). Keeping this issue open as tracked-but-blocked. The removal inventory (validation-only branches in bridge.py: _read_validation_hints, _discovered_operation, _models_conflict, _merge_parameters, _model_to_parameters, _field_type_to_schema, _is_base_model_type, the NAMESPACE_FALLBACK skew path, and the scan_validation_metadata alias) is ready to action once the gate clears.