feat(web): group sessions by machine and improve group headers

[gaius-codius]

Summary

Group sessions in the web sidebar by both machine and directory instead of directory alone, and improve the group header UI to make the machine context clearer.

Changes

• group session list entries by machineId + directory
• show a machine chip in each session group header
• resolve machine label from machine display name/host when available
• fall back to a short machine id when no friendly label is available
• keep expand/collapse behavior working with the new grouping key
• update group count logic to reflect machine-aware grouping

Why

When the same repo/path exists on multiple machines, the previous UI could merge those sessions into a single group, which made it unclear where a session was running. This change keeps those groups separate and makes machine context visible at a glance.

Validation

• verified visually in the local web UI
• confirmed sessions with the same path on different machines render as separate groups
• confirmed expand/collapse and session navigation still work
• ran bun run typecheck:web

[github-actions]

Findings

• [Major] Selected inactive sessions can disappear from the sidebar after this split. web/src/components/SessionList.tsx:375 still auto-collapses any group without an active session. After grouping by machineId + directory, an inactive selected session on machine A no longer stays visible just because another machine has an active session in the same repo.
  Suggested fix:

  const isGroupCollapsed = (group: SessionGroup): boolean => {
      const override = collapseOverrides.get(group.key)
      if (override !== undefined) return override
      const hasSelectedSession = selectedSessionId
          ? group.sessions.some(session => session.id === selectedSessionId)
          : false
      return !group.hasActiveSession && !hasSelectedSession
  }

Summary
Review mode: initial
1 issue found in the current diff.

Testing
Not run (automation). bun is not installed in this runner, so bun run typecheck:web could not be repeated here. Suggested coverage: a SessionList render case with two same-path sessions on different machines where the selected group has no active session and should remain expanded.

HAPI Bot

[github-actions]

Findings

• [Minor] The sidebar summary now counts (machineId, directory) groups, but the copy still renders that number as projects. One repo opened on two machines will now show up as 2 projects, which misstates what the counter means. Evidence web/src/router.tsx:117, related copy web/src/lib/locales/en.ts:42.
  Suggested fix:

  const sessionGroupCount = new Set(sessions.map(s => {
      const path = s.metadata?.worktree?.basePath ?? s.metadata?.path ?? 'Other'
      const machineId = s.metadata?.machineId ?? '__unknown__'
      return `${machineId}::${path}`
  })).size
  
  {t('sessions.groupCount', { n: sessions.length, m: sessionGroupCount })}

Summary
Review mode: follow-up after new commits
1 issue found in the current diff.

Testing
Not run (automation). bun is not installed in this runner, so bun run typecheck:web could not be repeated here. Not found in repo/docs: existing tests covering machine-aware sidebar grouping or the sessions counter copy.

HAPI Bot

[github-actions]

Findings

• None.

Summary
Review mode: follow-up after new commits
No actionable issues found on the current head. Residual risk: Not found in repo/docs: automated coverage for machine-aware grouping and selected-session auto-expansion in web/src/components/SessionList.tsx, or for the sidebar counter semantics in web/src/router.tsx.

Testing
Not run (automation). bun is not installed in this runner, so bun run typecheck:web could not be repeated here.

HAPI Bot