Third profiling round (after #66033 / #66347), targeting the composer
model picker and dialog opens (worktree dialog etc.), measured over CDP
on real 1000+-message sessions.
Backend — model.options took 4.8s cold / 1.8s warm per call, and the
desktop model pill/picker blocks on it every open:
- agent/credential_pool: _load_config_safe uses load_config_readonly().
Every consumer only reads, and the per-call deepcopy was the dominant
cost — list_authenticated_providers calls load_pool() per provider
row, and each load_pool loaded (and deep-copied) the full config
again via get_pool_strategy.
- hermes_cli/config: memoize ensure_hermes_home() per home path. It
runs inside the config lock on EVERY load_config(), paying ~14
mkdir/chmod syscalls per call. The fast path still re-checks that the
home dir exists, so a deleted home is recreated as before; profile
switches hit the new path and re-run. Tests cover both.
- tui_gateway/server: add model.options to _LONG_HANDLERS. It measured
seconds inline on the WS reader thread — while it ran, prompt.submit
and session.interrupt sat unread (same class as #21123).
Together: model.options RPC 4825/1842ms → 426/230ms (measured on the
live desktop backend); build_models_payload in isolation 6.2s → 0.97s
cold, 0.27s warm.
Desktop — every Radix dialog/popover open forced a whole-document style
recalc (Presence reads getComputedStyle on mount), which on a
1300-message transcript cost ~650-730ms per open (CPU profile:
getAnimationName 483ms self). The worktree dialog (⌘⇧B) paid it on
every single open:
- thread/list: content-visibility:auto + contain-intrinsic-size on the
per-turn group wrappers. Off-screen turns now skip style recalc,
layout, and paint entirely; never-rendered turns hold a placeholder
height (auto: remembered real size once rendered) so scrollbar and
anchoring stay stable. Verified over CDP: worktree dialog open 656-
730ms → ~200ms on the same session; stick-to-bottom pin, scroll-to-
top rendering, and sticky human bubbles all intact.
Also: profile-session-switch harness accepts CDP_HTTP (Chrome tends to
squat on 9222).
Verification:
- scripts/run_tests.sh: config, credential-pool, inventory,
model-switch routing, tui_gateway protocol, profiles suites green
(test_profiles has one pre-existing failure on main, unrelated);
new tests for the ensure_hermes_home memo.
- apps/desktop: tsc clean, eslint/prettier clean, thread + session
suites green (326 tests).
- E2E over CDP on the live app: numbers above, plus scroll/pin sanity.
Follow-up to #65890 (router transitions off) and #65898 (structural
compare + first-paint budget): profiling the switch path on real 1000+-
message sessions with a new CDP harness showed the remaining freeze is
NOT markdown rendering — it's a forced-reflow cascade from mount-time
layout reads interleaved with style writes across the transcript's
layout effects, plus the first-paint budget cut landing too late to
stop the full-budget commit.
Measured on the two largest local sessions (996 and 1363 messages),
main-thread longtask totals per switch: warm 2450ms -> 557ms and
1158ms -> 194ms; first paint 1690ms -> 444ms. Harness:
scripts/profile-session-switch.mjs (same CDP family as
profile-real-stream.mjs).
- use-resize-observer: drop the synchronous initial callback and ride
the observer's spec-guaranteed first delivery instead (same frame,
after layout, before paint). The sync call ran while the commit's
layout was dirty, so every size read in a callback forced a full
reflow — with one instance per user bubble (measureClamp read
scrollHeight, then WROTE --human-msg-full, re-dirtying layout for the
next bubble), the switch commit thrashed for over a second. Inside RO
timing the same reads are free. Composer metrics (2x
getBoundingClientRect + documentElement style writes) rides the same
fix.
- Same class, same fix at the remaining call sites profiling surfaced:
ExpandableBlock and TerminalOutput (dozens per tool-heavy transcript)
now measure/pin via RO initial delivery; the tool-window and
thinking-preview pins drop their sync pin() call; the thread
timeline's initial active-tick compute joins its existing
scroll-time rAF batching so back-to-back transcript updates coalesce.
- thread/list: cut the render budget in the RENDER phase (state-from-
props adjustment) instead of the post-commit layout effect. The
effect-time cut was too late — on a warm switch React first built and
committed the full 300-part tree, then re-rendered at 60, then bumped
back to 300, so the expensive commit still happened (and on a cold
switch the bump rAF usually fired while the transcript was still
empty, so the prefetched messages rendered at full budget anyway).
The render-phase cut restarts the component before any child renders;
a second trigger handles the cold path where messages land later
under the same sessionKey.
- thread/list: backfill 60 -> 300 inside startTransition so the older
turns' markdown+shiki render is interruptible background work instead
of a synchronous freeze one frame after the switch paints. Functional
Math.max so an urgent "Show earlier" click can't be rebased back down.
- composer focus: skip the rAF/timeout focus retries when the element
is already focused — focus() runs the full focusing steps (forcing
layout) even on the active element, ~585ms per switch on a large
dirty DOM.
- Replace the tautological render-budget test (it re-declared the
constants locally and asserted 60 < 300) with behavior tests of the
now-exported buildGroups + firstVisibleGroupIndex.
Verification: apps/desktop `npx tsc --noEmit` clean; full
`npx vitest run` 210 files / 1763 passed; manual CDP check confirms the
deferred backfill commits the full transcript, stays pinned to bottom,
and "Show earlier" still pages.
