refactor(progress-monitor): extract 4 single-responsibility modules from god class

[aaight]

Summary

Refactors src/backends/progressMonitor.ts from a 423-line god class with 5+ mixed responsibilities into a thin orchestrator (~245 lines) that composes four single-responsibility modules.

Card: https://trello.com/c/699dd8e10c3df6b4b67541ec

Extracted modules

• src/backends/progressState/accumulator.ts — Ring buffer state accumulation (ProgressAccumulator): tool calls, text snippets, completed tasks, iteration tracking, plus summarizeToolParams() and getSnapshot().
• src/backends/progressState/scheduler.ts — Progressive timer scheduling (ProgressScheduler): fires ticks at [1, 3, 5] min, then intervalMinutes steady-state. Pure scheduling — no business logic.
• src/backends/progressState/pmPoster.ts — PM comment lifecycle (PMProgressPoster): create-once / update-in-place / fallback-to-new pattern with state file coordination.
• src/backends/progressState/githubPoster.ts — GitHub PR comment updates (GitHubProgressPoster): session state lookup, comment formatting, and updatePRComment() call.

Changes to progressMonitor.ts

• Composes the 4 extracted classes — only orchestrates the tick flow (model call + posting + checklist sync)
• Public API unchanged: ProgressMonitorConfig, ProgressMonitor, ProgressReporter interface, start(), stop(), getProgressCommentId() all preserved
• All 44 pre-existing tests continue to pass without modification

New unit tests (46 tests across 4 files)

• accumulator.test.ts — Ring buffer bounds, param summarization, snapshot copies
• scheduler.test.ts — Progressive schedule, steady-state fallback, stop-during-tick safety
• pmPoster.test.ts — Create/update/fallback lifecycle, state file coordination
• githubPoster.test.ts — Session state lookup, comment body substitution

Test plan

• All existing tests pass (npm test → 3185 tests passing)
• 46 new focused unit tests added for each extracted class
• TypeScript type check passes (npm run typecheck)
• Lint passes (npm run lint) — pre-existing adapter.ts warning is unchanged

🤖 Generated with Claude Code

[nhopeatall]

✨ On it — checking the progress monitor refactor

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Progress: [███░░░░░░░] 30% (iteration 21/70)

🔍 Code Review Update (1 min)

I've completed a thorough review of the refactor/progress-monitor-extract-modules branch, examining the new progressState modules and confirming direct imports. I've also reviewed existing tests in tests/unit/backends/progress.test.ts to ensure continued functionality. My current focus is on understanding the initialization of ProgressAccumulator.startTime and how the start() method is called to ensure correct timing behavior.

_{Last updated: iteration 21 · review}

[nhopeatall]

LGTM — Clean extraction of a god class into four focused, single-responsibility modules. The decomposition preserves the original behavior faithfully, the public API is unchanged, and the new module boundaries (accumulation, scheduling, PM posting, GitHub posting) are well-chosen.

One minor observation (not blocking): ProgressAccumulator.startTime is now set at construction time (readonly startTime = Date.now()) rather than being reset in ProgressMonitor.start() as the original code did. In practice this is negligible — the gap between constructor and start() is milliseconds, and elapsed time is reported in minutes — but worth noting for completeness.

The 46 new tests cover each extracted module's key behaviors well, and all 44 existing integration-level tests continue to pass unchanged, which is strong evidence the refactoring is behavioral-preserving.