fix(web): scope chat resume reattachments

[LeonSGP43]

Summary

• add a dedicated resume helper that stamps a reopen nonce for session-list resume clicks
• scope dashboard chat attach tokens to the selected session/profile so switching sessions cannot reattach the previous PTY
• cover the URL and attach-scope helpers with targeted tests

Testing

• pnpm --dir web exec vitest run src/lib/chat-resume.test.ts
• pnpm --dir web exec tsc -p tsconfig.app.json --noEmit
• pnpm --dir web exec eslint src/pages/ChatPage.tsx src/lib/chat-resume.ts src/lib/chat-resume.test.ts
• git diff --check

Closes #62045

[alt-glitch]

This was generated by AI during triage.

Related to the wrong-session dashboard-chat PTY-reattach cluster (regression from the keep-alive PTY reuse in #60515):

• fix(dashboard): scope PTY attach token per resume session to prevent wrong-session reattach #61045 — earliest-open frontend fix (inline localStorage attach-token namespacing in ChatPage.tsx)
• fix(dashboard): scope chat attach tokens by session #60745 — backend fix (scopes the attach token by resume+profile in hermes_cli/web_server.py)
• fix(dashboard): force fresh PTY spawn when resume target changes #61313 — frontend force-fresh-spawn variant

This PR takes a different frontend mechanism (a dedicated chat-resume.ts helper + reopen nonce + SessionsPage wiring) and targets #62045. Not a duplicate — same goal, different layer/mechanism. Flagging the cluster so a maintainer can pick the layer(s) to land.

[teknium1]

Thanks for the focused frontend fix. The current-main diagnosis is valid: web/src/pages/ChatPage.tsx:61-81 keeps one global attach token, while hermes_cli/pty_session.py:148-166 reuses an existing live PTY solely by that token.

Problems

• The active-session reopen requirement in [Bug]: Dashboard chat session picker reopens the wrong session and cannot reopen the active one #62045 remains unsatisfied in the Chat right rail. web/src/components/ChatSessionList.tsx:113-129 returns immediately when id === activeSessionId, so it never emits the new resumeNonce. This PR adds nonce navigation only for the Sessions-page play action (web/src/pages/SessionsPage.tsx in 636d9b3f6bce).

Suggested changes

• Reuse the resume/nonce helper from ChatSessionList.pick() for every selected row, including the active row, and add coverage for that shared update path.

Automated hermes-sweeper review.