fix: stop retrying oversized requests and recover with one forced compaction

[hetaoBackend]

Problem

A request the provider rejects as too large fails the same way on every resend, but:

• The classifier mapped HTTP 413 to a generic upstream error. The API-key (minimax_api) and custom_provider:* paths retry every pre-output failure, so the same oversized body went out 6 times (~15 s of backoff). This also applied to request_too_large, the local pre-send check (Request body too large: … exceeds client limit …), and MiniMax invalid params, context window exceeds limit (2013).
• After that kind of failure the main turn never compacted and resent; it just failed.

Fix

• shared/llm-error-classifier: new request_too_large / context_overflow signals and isLLMRequestOversized(). HTTP 413, byte-limit rejections and unambiguous context-overflow messages are now deterministic rejections (sent once on every path). Transient shapes (timeouts, network errors, 408/429/5xx) are still excluded. A bare MiniMax 2013 without overflow wording is not treated as an overflow.
• agent-core: new PiTurnHooks.contextOverflowRecoveryHook. When a main-agent request is rejected as too large before any output (pi-ai isContextOverflow or isLLMRequestOversized), the runner runs only these hooks, once per turn, with trigger: 'context_overflow_recovery'. It then persists the replacement through the normal history path and resends once. A second rejection, or a recovery that changes nothing, surfaces the original error. The rejected attempt never reaches history, and ordinary before-LLM hooks (reminders and so on) do not run twice. The wrapper sits inside the logical-call metrics and capture.
• local-runtime-v2: the executor registers the automatic compaction hook (with its plugin lifecycle) as the recovery hook. The trigger forces compaction regardless of the local estimate and caps the result at 50% of the rejected request's measured tokens/bytes, because the estimate had admitted a request the provider rejected.
• No image-specific recovery is added; image normalization is handled separately.

Tests

• llm-retry.test.ts: oversized shapes (413 variants, request_too_large, local body check, 2013 overflow, prompt too long) are sent once on minimax_api, custom_provider, and the managed path. Added classifier positive/negative cases, including the BYOK-attributed form.
• New context-overflow-recovery.test.ts (PiTurnRunner end to end):
  • a 413 leads to one compaction and one resend, and the turn completes;
  • if the resend also fails, the turn fails with the original error;
  • a recovery hook that changes nothing means no resend;
  • non-size errors don't trigger recovery;
  • ordinary hooks are not re-run;
  • with no hook installed, behavior is unchanged.
• automatic-context-compactor.test.ts: the forced trigger starts compaction below the thresholds, and the hook maps the runner trigger to force.
• pnpm typecheck, node scripts/run-vitest-suite.mjs capability (215 files, 5406 passed), and check:source all pass.

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[yujiachen-y]

LGTM