Dual-gate (Codex + Opus) findings on the Claude Code transcript parse cache:
1. Cache-key staleness hardening: add st_ctime_ns to the (path, mtime_ns, size,
max_messages) key so a rare same-size, same-mtime in-place edit can't serve a
stale parse. Size is already the strong discriminator for append-only JSONL;
ctime_ns is cheap defense-in-depth (a spurious bump costs one harmless re-parse,
never a stale read).
2. Timestamp-fallback bug-for-bug fix: the row-builder guard used identity
(first_ts is None and last_ts is None) but the field assignment uses truthiness
(first_ts or last_ts or _mtime). They disagreed on a falsy 0.0 timestamp
(epoch-0/1970 transcripts), leaving created_at/updated_at/last_message_at = None
instead of the file mtime the pre-cache inline code fell back to. Guard now uses
the same 'not first_ts and not last_ts' test.
Adds 3 regression tests: epoch-0 mtime fallback, the shared-dict read-only
contract (pins the load-bearing invariant), and same-size+mtime ctime invalidation.
The /api/sessions cold build (which a profile switch triggers) was
dominated by get_claude_code_sessions() re-parsing every Claude Code
JSONL transcript line-by-line on each call — 650-1000ms on a 200-file
/ ~130MB tree, repeated on every switch, every 5s CLI-cache expiry, and
every sidebar poll, because the directory is global but the higher
session cache is keyed per active profile.
Memoize the per-file parse by (path, mtime_ns, size) so a warm build
re-stats files instead of re-parsing them; any genuine edit/append
changes the stat signature and invalidates just that file. Also hoist
the loop-invariant get_last_workspace() out of the Claude Code row loop
(it stats config + probes terminal cwd, ~200 redundant calls per build).
Measured /api/sessions cold-rebuild on a 250-session profile: ~670-880ms
-> ~100-200ms (verified in-browser). Output byte-identical.
Credit @rodboev for the browser-level profiling that isolated the real
bottleneck (the prior pre-warm hypothesis could not move it).
Co-authored-by: rodboev <rodboev@users.noreply.github.com>
nesquena-hermes