Small unbounded growth: paste-debug registry, empty proxy dirs, autosave bundle ledger, workflow maps, lastActivityAt, conversation caches, CLI update logs #1278

Grouped P3s from the C6 hunt:

• pasteDebugJournal.ts journals Map never deleted (dispose has no callers); 1,082 files on disk.
• debugRetention deletes only the leaf proxy run dir: 2,978 empty dirs remain, and the walk goes 4 levels on every prune.
• debugBundleLog autosaved-debug-bundles.jsonl is append-only, never trimmed; the legacy 18.4 MB saved-debug-bundles.jsonl is re-parsed on every prune.
• WorkflowBridge runsBySession / latestLifecycleByRunId never delete per session/run.
• sessionManager lastActivityAt kept after removal on purpose, never evicted.
• conversations service promptCache / claude summaries / codex heads+rolloutPaths have no LRU.
• cli-update-logs/*.log have no retention.
• windowRegistry retiredWebContentsIds never evicted.
• worktree-activity-index.json is 91.5 MB, rewritten whole on refresh (perf(diagnostics): default-off and off-thread the always-on diagnostic subsystems #767 item 3 covers part).

Found by the Stage 3 C6 hunt; lines are origin/main 9c6e48f. Findings file: temp/quality-loop/hunt-c6.md.

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