[BUG] Desktop: local session transcripts grow unbounded and freeze the UI when opening heavy sessions; sidebar "Delete" does not remove transcript files

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Environment: Claude Desktop 1.37937.3 (Windows 11 Home 10.0.26200, x64), bundled Claude Code 2.1.246, 32 GB RAM (~21 GB free while the issue reproduces), 20-core CPU.

Heavy local-session usage (long agentic sessions with hundreds of subagents) degrades the desktop app until typing lags for seconds, even though system memory and CPU are mostly idle. Four compounding behaviors:

1. No usable lifecycle policy for local transcripts. ~/.claude/projects/<project>/ had grown to 7.9 GB / 5,100+ files across 71 sessions, with transcripts persisting since February. A single finished session held 3.1 GB (84 MB main transcript + 298 subagent transcripts). The only existing mechanism, cleanupPeriodDays (default 30), never swept anything here — notably, old transcripts' mtimes appear to get refreshed in clusters (dozens of .jsonl from March–July all sharing the same few minutes of mtime), which would defeat mtime-based cleanup. So in practice nothing ages out, compacts, or archives.

1. Opening a heavy session parses tens of MB of JSON on (or blocking) the UI thread. Selecting such a session in the sidebar freezes input for seconds; while it stays open the app feels "about to crash". RAM is not the issue (app tree ~2 GB, 21 GB free) — it is CPU on the interactive path.

1. Sidebar "Delete session" removes only the list entry. The .jsonl and the <session-id>/subagents/ folder remain on disk, so users who delete heavy sessions to fix the slowdown reclaim nothing, and there is no in-app way to actually free the space. (Deleting the same session from claude.ai web did remove the local transcript — the surfaces behave inconsistently.) Together with #86730 (sidebar advertises sessions whose files were silently deleted), the sidebar and the transcript store are out of sync in both directions: it keeps files for sessions the user deleted, and lists sessions whose files are gone.

1. Full transcript rescan at startup — the stats worker walks every transcript file on each launch, which keeps getting slower as sessions accumulate.

Startup log excerpts (%LOCALAPPDATA%\Claude\Logs\main.log, ids redacted):

[warn] [CCD] Session <id> transcript is 84219319 bytes; tail-loading last 52428800 bytes
[warn] [CCD] Session <id>: subagent transcripts exceed the load bounds (33554432 bytes, 256 pending); loaded 5 of 298 (33554432 bytes), 0 pending, skipped 293
[info] [CCD] /stats (worker) scanned 2344/2344 transcript files since 2026-02-26

Impact: persistent input latency and multi-second freezes for a heavy daily user on an idle 32 GB machine. Manually deleting transcript files from disk (after extracting a small text digest) reduced the folder from 7.9 GB to 2.1 GB and restored responsiveness, confirming transcripts as the cause.

Repro sketch: accumulate a few sessions of >500 MB (long agentic runs with many subagents) → restart the app and open one from the sidebar → typing freezes while it loads and the warnings above appear in main.log → delete the session from the sidebar → files remain under ~/.claude/projects/.

Related: #86730 / #87748 (silent mtime-based deletion — the mirror-image lifecycle failure, arguing for an explicit, user-visible retention design rather than the current extremes), #81065 (transcript compression on disk — addresses storage size but not UI-thread loading, lifecycle, or delete behavior).

What Should Happen?

1. Transcript lifecycle policy: auto-archive or compact old finished sessions (e.g., after N days keep a digest and compress/offload subagent transcripts), with a retention setting.
2. Sidebar delete should free space — or offer a "delete including local files" option and clearly say when files are retained.
3. Parse transcripts off the interactive path (worker thread / incremental hydration) so opening a large session never blocks typing.
4. Incremental stats indexing instead of a full rescan of every transcript at each launch.

Error Messages/Logs

Steps to Reproduce

1. Use the Claude Desktop app for months of heavy agentic work so ~/.claude/projects/<project>/ accumulates several sessions larger than 500 MB (long runs with hundreds of subagent transcripts).
2. Restart the app and open one of those sessions from the sidebar → typing input freezes for seconds while it loads; %LOCALAPPDATA%\Claude\Logs\main.log logs the tail-loading / subagent transcripts exceed the load bounds warnings quoted above.
3. Delete that session from the sidebar → its .jsonl and <session-id>/subagents/ folder remain under ~/.claude/projects/ and no disk space is reclaimed.
4. Observe startup cost grow with session count: /stats (worker) scanned 2344/2344 transcript files.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.246 (bundled in Claude Desktop 1.37937.3; observed in the desktop app)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

_No response_