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>
