auth.json is rewritten by credential-pool/OAuth token refresh roughly every
14 minutes. _models_cache_source_fingerprint() hashed it via mtime/size
(#1699 _models_cache_file_fingerprint), so every token refresh churned the
fingerprint and the 24h /api/models cache was effectively dead -- the hot
GET /api/session?resolve_model=1 path paid a cold ~11.5s rebuild every few
minutes (RCA t_d127953d residual #2, t_16551f61).
Add _auth_store_semantic_fingerprint(): content-hash auth.json with a
DENY-list of known credential-rotation-only keys (access/refresh token,
expiry, per-credential status/telemetry, request_count, save updated_at)
stripped. Deny-list (not allow-list) is deliberate -- any unknown field, or
a real provider/endpoint/model-set change (active_provider, a new
credential_pool entry, base_url, source, label, auth_type, the providers{}
block, ...) stays in the fingerprint and still correctly busts the cache.
Conservative fallbacks: missing file -> marked; unreadable/corrupt ->
stat-based fallback (never less safe than pre-fix). config.yaml keeps the
cheap stat fingerprint (deliberate edits, no timer churn).
Bidirectional invariant regression test (non-tautological -- the
end-to-end churn test flips RED when the auth_json axis is reverted to
stat-based): token-only churn keeps fingerprint byte-identical AND keeps a
valid disk cache loadable; active_provider change / new credential_pool
entry / changed base_url each flip the fingerprint AND reject the stale
disk cache. Measured: 5/5 cold rebuilds per 5 refresh cycles -> 0/5.
Tests: 9 new pass; 28 adjacent (#1699/#1633/display-resolver) pass;
54 models_cache/fingerprint suite pass.
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