Harden single-candidate gemini recovery

TODO.md

@@ -655,6 +655,24 @@
 - If behavior in the browser does not match the latest backend/frontend code, the first assumption should be stale frontend assets until proven otherwise
 
 ## Recent Change Log
+- Date: `2026-03-17`
+- What changed:
+  - Added a dedicated single-candidate Gemini recovery path that no longer asks for JSON and instead parses a tiny plain-text key/value response.
+  - Kept multi-candidate Gemini Vision on compact JSON, but changed sequential recovery to use the shorter plain-text format automatically through the existing `Recommend(..., []SearchResult{item})` path.
+  - Added unit coverage for the single-candidate plain-text parser.
+- Why it changed:
+  - The user-provided log `ai-media-hub-2026-03-17T08-20-31-074Z.log` showed even more severe truncation:
+    - `"{\"recommendations\":[{\"index\":"`
+    - `"{\"recommendations"`
+    - `"{\"recommend"`
+  - The same log showed `sequentialRetried: 0`, which means the old single-candidate recovery path was still too verbose and was not successfully rescuing failed batches.
+- How it was verified:
+  - `pwsh -NoProfile -File scripts/selftest.ps1`
+  - added Go tests for single-candidate Gemini plain-text parsing
+- What is still risky or incomplete:
+  - If Gemini returns malformed plain text that omits the required `verdict:` line, even the single-candidate recovery path can still fail.
+  - This improves recovery robustness, but total Gemini latency can still rise when many batch failures fall back to candidate-by-candidate evaluation.
+
 - Date: `2026-03-17`
 - What changed:
   - Added adaptive Gemini Vision output-token sizing so smaller candidate batches, especially single-candidate sequential recovery calls, now request much shorter responses.