ops: free-tier deepseek flip evidence

docs/operations/free-tier-deepseek-flip-20260803.md

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+# Free tier flipped to deepseek-v4-flash (2026-08-03)
+
+## Why
+
+The free tier was hard down: the production Gemini key returns HTTP 429
+"monthly spending cap exceeded" (recorded in
+[`dep-prod-disabled-20260803.md`](dep-prod-disabled-20260803.md)). The
+deepseek-0731 remeasurement chain
+([`serving-engine-deepseek-0731-correction-20260803.md`](serving-engine-deepseek-0731-correction-20260803.md))
+established gate parity at ~1/8 the cost, and the owner approved the
+free-tier switch on 2026-08-03.
+
+## Validation before the flip
+
+- 22 fixtures × `--repeat 3` at `reasoning_effort: low`: 17 pass / 2 warn /
+  3 error on worst-of-three status; every MEDIAN score clears the floors
+  (lowest median MPS 80). The three errors are single below-70 MPS samples on
+  `en-email-01` / `ko-blog-01` / `ko-news-01` — per-run variance, not a
+  register failure. In production such a sample is refused by the MPS floor
+  gate (customer sees a retryable error), never delivered silently.
+- Code: PR #677 (reviewed) — rewrite reasoning cut scoped to free+deepseek,
+  scorer cut extended to deepseek, streaming extraBody passthrough. Shipped
+  to main via release PR #678.
+
+## The flip
+
+Vercel env (preview 2026-08-03, then production after #678):
+`PATINA_FREE_PROVIDER=deepseek`, `PATINA_FREE_MODEL=deepseek-v4-flash`,
+`PATINA_FREE_API_KEY=<deepseek key>`. Explicit redeploy after the env change.
+
+## Post-flip production smoke (patina.vibetip.help)
+
+| probe | result |
+|---|---|
+| free ko rewrite | 200, 34.2s end-to-end, MPS 100, fidelity 100 |
+| number safety | `14:30`, `23,000` preserved |
+| scaffold leakage | none (`[SELF_AUDIT]` absent) |
+| pro unknown license | 403 `license not entitled` (Polar gate intact) |
+| launch config | still the disabled shape |
+
+## Standing notes
+
+- The Pro tier still runs gemini-3.6-flash on `PATINA_PRO_API_KEY`; if that
+  key shares the capped Gemini project, Pro serving is still blocked until
+  the owner clears the spend cap — unverifiable without a live license.
+- Rollback: restore the three `PATINA_FREE_*` values to the gemini set and
+  redeploy (values retained in the secret manager history).
+- Watch item: DeepSeek announced (date TBA) 2x peak-hour output pricing;
+  reassess cost if activated.