perf(web): mount session row dialogs only while they are open

[hqhq1025]

Problem

Every SessionItem renders its rename dialog and both confirm dialogs unconditionally, passing isOpen to keep them closed (SessionList.tsx). With 28 sessions that is 84 mounted Radix dialogs the user cannot see, and each carries a Presence / DialogProvider / DialogContent / DialogPortal subtree that re-renders whenever the row does.

Measured against a live hub, those dialogs were roughly half of the entire fiber tree — 1680 nodes before, 886 after. Profiling a single machine-updated event (arrives every 20s per machine, carries only changed CPU/memory numbers) showed it re-rendering 1600+ dialog-internal components:

Presence               3360
Dialog                 1680
DialogProvider         1680
DialogContent          1680
DialogPortal           1680
ConfirmDialog           848
RenameSessionDialog     416

Fix

Mount them on demand. The same file already does this for SessionExportDialog and the reopen-error ConfirmDialog, so this only brings the remaining three in line with the pattern sitting right next to them.

dialog.tsx has no open/close transition (its only transition-* is the close button's hover color), so nothing animates on unmount.

Measured effect

Real Chromium against a live hub, 70s steady state, stacked on top of the activeAt patch fix (#1232). The fiber-tree number is attributable to this change alone:

	before	after
fiber tree	1680	886
components re-rendered	54k	15.5k
long tasks	26 / 2713ms	0 / 0ms
main thread blocked	3.6%	0.0%
frame rate	58.4 fps	59.8 fps

Long tasks disappear entirely.

Verification

Driven interactively in a real browser with real pointer events, not synthetic clicks:

• idle: 0 dialogs in the DOM (was 84)
• long-press a row → menu opens with Rename / Copy reference / Export conversation / Archive
• click Rename → dialog opens, input prefilled with the current session name
• Escape → dialog closes, back to 0 in the DOM

Testing

• tsc --noEmit -p web/tsconfig.json clean
• Full web suite: 1598 pass, 0 fail

[github-actions]

Findings

• None.

Summary

• Review mode: initial
• No correctness, security, regression, data-loss, performance, or maintainability issue found in the added/modified lines.
• Residual risk: no automated SessionItem coverage asserts that rename/archive/delete dialogs remain unmounted while closed and still complete their open/close flows.

Testing

• Not run (automation); PR code was not executed under the review security policy. The PR reports web typecheck and 1,598 passing web tests; the GitHub test check was still in progress when reviewed.

HAPI Bot