Greptile Summary

This PR fixes a bug where the pi-coding-agent library's auto-compaction mechanism would never trigger when a user-configured agents.defaults.contextTokens cap (e.g. 160k) was significantly smaller than the model's native context window (e.g. 1M for Gemini Flash). The fix constructs an effectiveModel object with contextWindow overridden to ctxInfo.tokens (the resolved effective limit) and passes it in place of the raw model to the agent session and tools, ensuring the library's internal threshold calculation uses the correct, capped value.

Key changes:

• run.ts: Derives effectiveModel immediately after the existing resolveContextWindowInfo call and passes it to runEmbeddedAttempt instead of the raw model.
• compact.ts: Adds a new resolveContextWindowInfo call (not previously present in the compaction path) to derive effectiveModel, and applies ctxInfo.tokens to both modelContextWindowTokens in createOpenClawCodingTools (fixing a secondary issue where model.contextWindow could be undefined) and model in createAgentSession.
• compact.hooks.test.ts: Adds the missing DEFAULT_CONTEXT_TOKENS export to the ../defaults.js mock to prevent test failures from the newly introduced resolveContextWindowInfo call in compact.ts.
• The effectiveModel only overrides contextWindow; all other uses of the original model (.api, .provider, .id) remain unchanged and correct.

Confidence Score: 5/5

• This PR is safe to merge — it applies a well-scoped, minimal fix to a clear compaction threshold bug with no side-effects on other model properties.
• The change is minimal and surgical: it only overrides contextWindow on a locally-scoped copy of the model object. All other model properties (provider, api, id) continue to come from the original model. The ?? Infinity guard correctly handles models without a declared context window. The test mock fix is accurate. Both affected code paths (run.ts and compact.ts) are handled symmetrically, and no existing logic is removed — only the downstream recipient of the model object is updated.
• No files require special attention.

_{Last reviewed commit: 26f658e}

Landed on main.

What we did:

• Landed the compaction context-window cap fix from this PR.
• Added changelog entry in 2026.3.7 Fixes with contributor + PR reference.
• Ran full gate before landing:
  • pnpm lint
  • pnpm build
  • pnpm test

SHA details:

• PR head reviewed: 26f658eef6564bd4f5476b6d8f6c454b1b7aada5
• Landed on main: 537c97cce

Thanks @MumuTW for the fix.