[v2] Make compaction summaries structured and economical

[SivanCola]

Summary

Change compaction summaries to a fixed five-section structure and skip summarization when the compactable region is too small to be worthwhile.

Root Cause

Free-form summaries are harder for the agent to resume from, and compacting very small regions can cost more latency and tokens than it saves.

Technical Approach

Update the summarizer prompt to emit Goal, Decisions, Files, Commands, and Pending sections; wrap summaries in a dedicated tag; add a simple fold-economics threshold.

Focused Optimization Points

• Improves resumability after compaction.
• Makes compacted summaries easier to distinguish from live user input.
• Avoids low-value summarization calls for tiny regions.

Verification

Not run during this publishing pass. This is opened as a draft PR for upstream review of the split branch.

[chatgpt-codex-connector]

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[SivanCola]

Resolved the merge conflict by merging the latest main-v2 (ee44f479) into feat/compact and pushing the PR branch to 58cf203c.\n\nWhat was preserved:\n- Kept the PR's structured/economical compaction behavior and tests.\n- Brought in the latest checkpoint, rewind, controller, desktop bridge, and locale updates from main-v2.\n- Let Git's merge combine internal/agent/compact.go without manual conflict markers remaining.\n\nVerification run locally:\n- go test ./...\n- npx pnpm@9 install --frozen-lockfile && npx pnpm@9 build\n\nGitHub checks are currently pending for macOS and Ubuntu.