fix(tui-gateway): restore openrouter provider override on session.resume

[Ahmett101]

Summary
_BARE_BILLING_PROVIDERS at tui_gateway/server.py:2011 incorrectly bundled "openrouter" with the real bare buckets "auto" and "custom". OpenRouter is a fully routable provider — it owns the session's API key, base_url, and live model catalog — so dropping its billing provider on session.resume silently redirected the restored model through whatever the user's current config default was (typically a newly-added custom endpoint like Featherless). That endpoint then probed its own /v1/models for the restored Opus model's context length, didn't find Opus, and surfaced as "context window of 2,048 tokens, which is below the minimum 64,000 required by Hermes Agent". Fixes #57588.

Fix: drop "openrouter" from the bare set. The remaining two bare buckets ("auto" global-default sentinel, "custom" unnamed billing class) stay filtered because restoring either as a provider override breaks resume for the documented reason — "auto" defeats session-scoped restore, "custom" is non-routable and surfaces as "No LLM provider configured".

Composition note: this fix is independent of the in-flight #57503 (picker filter) and #50289 (first-class mistral plugin). All three merge cleanly with no overlap; the bare-bucket set in tui_gateway does not interact with the picker or provider plugin registries.

Changes

• tui_gateway/server.py: drop "openrouter" from _BARE_BILLING_PROVIDERS, expand the docstring to spell out why each of the two remaining bare buckets is bare and why openrouter is not. Single conceptual change: {"auto", "openrouter", "custom"} → {"auto", "custom"}.
• tests/test_tui_gateway_server.py: update test_stored_session_runtime_overrides_skips_bare_billing_provider — "openrouter" is now removed from the bare-tuple loop and added as a positive assertion (ov["provider_override"] == "openrouter").
• tests/tui_gateway/test_custom_provider_session_persistence.py: add two tests under TestBareCustomNoBaseUrlHealsFromConfig:
  • test_restore_preserves_openrouter_billing_provider — pins the bug. row.model=anthropic/claude-opus-4-8, row.billing_provider="openrouter" → overrides["provider_override"] == "openrouter" AND overrides["model_override"]["provider"] == "openrouter". Failure mode reproduces the reporter's "context window … below 64,000" error.
  • test_restore_drops_auto_billing_provider — companion negative check that the "auto" sentinel stays filtered (resume falls back to the configured default for bare "auto").

How to Test

# new + updated regression suite
pytest tests/tui_gateway/test_custom_provider_session_persistence.py::TestBareCustomNoBaseUrlHealsFromConfig::test_restore_preserves_openrouter_billing_provider \
       tests/tui_gateway/test_custom_provider_session_persistence.py::TestBareCustomNoBaseUrlHealsFromConfig::test_restore_drops_auto_billing_provider \
       tests/test_tui_gateway_server.py::test_stored_session_runtime_overrides_skips_bare_billing_provider -xvs
# 3/3 passed

# broader suite to confirm no regressions
pytest tests/tui_gateway/test_custom_provider_session_persistence.py \
       tests/tui_gateway/test_billing_rpc.py \
       tests/tui_gateway/test_finalize_session_persist.py \
       tests/test_tui_gateway_server.py -q
# 346/346 passed

Bug-catch verification (the new regression test catches the bug):

git stash push -m bug-check tui_gateway/server.py
pytest tests/tui_gateway/test_custom_provider_session_persistence.py::TestBareCustomNoBaseUrlHealsFromConfig::test_restore_preserves_openrouter_billing_provider -vs
# FAILS: AssertionError — provider_override dropped on resume (the exact symptom #57588 reports)
git stash pop

Checklist

• Tests pass — 3 directly + 343 sibling picker/session tests, 346/346 green
• Follows Conventional Commits (fix(scope):)
• Single-purpose: one-line semantic change in _BARE_BILLING_PROVIDERS, doc update, test coverage
• Cross-platform impact: None (pure Python constant + dict-shape session data, no environment-sensitive code)
• profile-safe paths: N/A (no paths touched)
• .env not used for non-credential settings: N/A
• No new dependencies
• Composes with [Bug]: mistral listed in /model picker but fails with "Unknown provider 'mistral'" #57503 and feat: add Mistral AI as first-class LLM provider #50289 — no overlap

Risk & Impact
Low. Strictly removes a spurious continue-equivalent in a session-restore path: stored OpenRouter rows now come through with their provider override intact instead of being silently dropped. Users who currently hit the bug get a fixed resume immediately; users with working environments see no change. The two real bare-bucket cases (auto, custom) still filter identically to before.

Type: Bug fix
Closes #57588

Related findings (out of scope here, flagged for maintainers):

• The historical commit (e256f4a per the reporter's analysis) appears to have intended only "custom" but bundled "openrouter" along for what was likely a "route via OpenRouter if any credential resolves to OR" mental model. If a similar bundling exists elsewhere (e.g. a sibling bare-bucket check that mistakenly skips "anthropic", "google", or other routable names), an audit pass driven by the now-shrunk _BARE_BILLING_PROVIDERS semantics would surface it. Strictly out of scope for this PR; happy to file/follow up if asked.
• A future micro-bench step in the resume path could call resolve_provider_client("openrouter", ...) as an early sanity check rather than deferring to agent_init's 64K-context guard, but that's a hermes_init-level change and depends on design buy-in.

[alt-glitch]

This was generated by AI during triage.

Duplicate of #57593 — both PRs fix #57588 with the byte-identical change (drop "openrouter" from _BARE_BILLING_PROVIDERS in tui_gateway/server.py). #57593 was opened first (07:56Z vs 08:05Z), so it is the canonical version; only the docstring wording differs. Cross-linking so a maintainer can pick one.