#137 fix(opencode): retry output-limit responses

Summary

• retry output-limit responses with at most three total LLM calls
• resample the identical LLM request object without adding a continuation message
• replace only attempts that will actually be retried, while rolling their billed usage into one final persisted step-finish record
• preserve the third call's partial output when all attempts truncate, matching Cloud's intentional partial-result-plus-error behavior
• leave existing retry behavior for rate limits, transport failures, and provider 5xx responses unchanged

Production evidence

Four V4 runs in the audited 12-hour window ended at provider output limits. None made another LLM request; two had no extractable answer and two retained only a truncated partial answer.

Historical behavior

• output partials have been persisted since the 2025-11-17 agent-loop refactor
• Cloud PR #5002 intentionally returns a final truncated partial next to its failure
• generic retries were originally bounded at 10; the same 2025-11-17 refactor replaced that loop with an unbounded one

Validation

• bun test test/session/retry.test.ts (34 passed)
• targeted processor regression proves identical input, one final persisted boundary, and combined usage (1 passed)
• real local bcode run: successful resample made 2 calls; exhausted resample stopped at exactly 3 calls and exited 1
• the plain CLI stdout streams partial attempts before cleanup; Cloud's final result is extracted from the cleaned persisted transcript
• package and root typecheck passed with Bun 1.3.14 (16/16 root tasks)
• targeted oxlint: 0 errors