fix(tui): drop cross-session events during null-sid switch window (#51058)

[yingliang-zhang]

Problem

During session switch/reset, getUiState().sid is momentarily null. The old event filter ev.session_id && sid && ev.session_id !== sid short-circuits to false when sid is null, so events from any live session bleed into the view — the cross-session bleed reported in #51058.

Fix

Change the condition so that when sid is null, all non-gateway session events are dropped:

- if (ev.session_id && sid && ev.session_id !== sid && !ev.type.startsWith('gateway.')) {
+ if (ev.session_id && (!sid || ev.session_id !== sid) && !ev.type.startsWith('gateway.')) {

(!sid || ev.session_id !== sid) means: drop the event if there is no active session or the event belongs to a different session. Gateway-meta events (gateway.*) are still always allowed through.

Scope

1 file, 1 condition change. Supersedes #53928 which was opened from a main branch and accidentally bundled 3 unrelated fixes.

Closes #51058

[tonydwb]

Code Review Summary

Verdict: Approved

Clean one-line fix for cross-session event bleed during null-sid switch (#51058). The change from ev.session_id !== sid to !sid || ev.session_id !== sid ensures ALL non-gateway session events are dropped when sid is null (during session switch/reset). This prevents another live session's events from bleeding into the view.

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Reviewed by Hermes Agent

[teknium1]

Thanks for isolating the TUI routing window; current main still has the null-sid short-circuit at ui-tui/src/app/createGatewayEventHandler.ts:407, and resetSession() does set sid: null at ui-tui/src/app/useSessionLifecycle.ts:159.

Problems

• The proposed predicate starts with evSid && (ui-tui/src/app/createGatewayEventHandler.ts:418 in this diff), so session_id: '' bypasses it. That does not implement the PR's stated empty-string filtering.
• The new negative tests do not exercise transcript routing. message.delta only records buffered state (ui-tui/src/app/createGatewayEventHandler.ts:939-942); assistant messages are appended on message.complete (:943-949). The new cases send only a delta before asserting no appended assistant message. The length >= 0 checks are tautological.

Suggested changes

• Preserve the null-sid fix, and align the empty-ID behavior with a verified event contract.
• Make the regression tests send a sequence that would append without filtering, including message.complete, then assert the transcript remains unchanged for rejected sessions.

Automated hermes-sweeper review.

[yingliang-zhang]

Addressed the automated review in a4965755413ec9d9e2c4a9080c8725b1b99812cd.\n\n- Distinguished a truly absent session_id (unscoped) from an explicitly present empty ID (invalid scoped event).\n- Non-global explicit empty/foreign events are rejected unless they match the active session; global skin events remain accepted.\n- Replaced tautological checks with real message.delta + message.complete transcript sequences.\n- Full affected Ink file: 83 passed, 0 failed. Typecheck, scoped ESLint, Prettier, and git diff --check passed.