[currentbits]

Part of #1475 (deep dive into PM3's Electron-only renderer heap growth). The full write-up is docs/perf/2026-10-06-electron-heap.md.

Finding: the unbounded growth is not a bridge or IPC leak. It is the stick-to-bottom pin loss that #1491 fixed: a trim's scrollTop clamp reads as the user scrolling up, so the window never trims again.

In a 30-stream Electron soak on main before #1491, the pin was lost at stream 10:

	Stream 9	Stream 30
JS heap	44 MB	154 MB
DOM nodes	12k	175k
vmmap footprint	~150 MB	482 MB

With #1491, two 30-stream runs stayed pinned: heap 39–46 MB, DOM 12–13k and footprint 141–149 MB, flat from stream 6 to 30.

This PR's fix (clampWindowStart): when the store's retention cap drops a long thread's head, an unpinned window whose start was past the new length used to reset to the last 120 entries regardless of size. That mounted 48k nodes at once in the soak. It now resets to tailWindowStart, the character-budgeted tail.

Where PM3's +12 MB came from (all of it bounded):

• the first thread:updated after launch is a full 4 MB transcript, released by stream 6;
• the markdown parse cache reaching its 400k-char budget;
• V8 code-space warm-up.

PM3's "RSS peak 416 MB" was ps RSS noise; the vmmap footprint is the reliable number.

Verified independently, on main merged with this branch

• typecheck exits 0 and vite build passes.
• test:renderer passes 2754 of 2754.
• The new transcriptWindow.test.ts cases fail on main (2 of 8).
• The branch predates fix(thread): a trim's scrollTop clamp no longer unsticks the transcript (#1475) #1491; the merge is clean and keeps it.

Safety: 18 Electron launches on the PM3 zero-leak recipe, each followed by a leak check, with no clone git writes and no recovered/*. The halts were attributed to live activity: an orchestrator worktree, the #1491 push, and a botpoc commit.

🤖 Generated with Claude Code

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-06T12:55:38.311688Z	9edff02	PR opened

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review" or "@codex security review".

Codex reacts with 👀 while any review is running, comments if it has suggestions, and reacts with 👍 once all reviews finish with no findings.