#26885 fix(webviews): relay local daemon peer state events

Local daemon peer transitions currently do not reach the web session's peer state. This narrow source PR intentionally extracts and replaces the stale peer-state carrier in our existing remote-location strip draft #26796 (b749e778f5bb2203333556be9a53ff1437095dc1), which also carries unlanded picker prerequisites. #26796 remains draft and must rebase onto this foundation and remove its superseded carrier hunks before review. This PR supplies the carrier foundation; remote-strip UI completion and real-machine proof remain outstanding.

The owning overlap index covered 482 open PRs. The feature overlap is our own #26796; other overlaps are shared transport or native allowlist files, with no other peer-state adapter identified. This change leaves picker presentation, optional-project behavior, recent folders, defaults, colors, and glass untouched.

The adapter follows the merged daemon contracts from #26756 (honest initialize handshake), #26823 (peer-state events), and #26860 (origin privacy). It enables only when initialize advertises peerStateEvents and reports the local origin used by LOCAL/APP connections. Peer, remote, missing, and unknown origins cannot request or consume peer topology.

• Read _acpmux/peers {} once after initialization and on each reconnect, then apply _acpmux/peer_state_changed from that same connection. No polling.
• Fence snapshots by connection/read generation and per-peer revision so an older read cannot overwrite a newer event. Repeated identical observations remain idempotent while still fencing stale reads. Explicitly clear old lastSeen and error values, and reset capability before a reconnect initializes.
• Add only the missing native _acpmux/peers relay, accepting no parameters and filtering replies to name, state, lastSeen, and error. Existing incoming notification forwarding carries the events. No daemon or session/auth fallback changes.
• Preserve existing snapshot behavior when the feature is absent.

Validation on Linux at 085467e71042c174e90a7b7a2d748e04e502be08 over 1f723c64fe2a70709ac21b88f10f4bc8bfdf0823: meaningful tests-first red was 3 failures / 4 passes; the repaired integration and reducer suites pass 15 tests / 66 assertions. Full bun --bun run check passes. The supported scoped web prepush helper passes under Bun, and the permitted source-scanner prepush layers report no new violations across all eight changed files. Native policy tests are included but unrun.

The #26809 hold is lifted. No real remote-machine transition, spinner/green/red, no-project Send, light/dark, or gallery capture has been verified. Root owns fresh independent exact-head review, required-check reconciliation, and the final landing loop. Our existing #26796 remains unchanged.

Agent session: agent session

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Summary by cubic

Relays local daemon peer state events to the web session's peer state, so peer transitions on the local machine show live instead of only at the last _acpmux/status read.

• Adds a zero-parameter _acpmux/peers native relay that filters replies to name, state, lastSeen, and error.
• The web client reads one snapshot after initialize and on each reconnect, then applies _acpmux/peer_state_changed notifications; it never polls.
• Enables the feature only when initialize advertises peerStateEvents and the origin is local/app; other origins and older daemons keep the existing snapshot behavior.
• Fences snapshot reads per connection/read generation and per-peer revision so stale reads cannot overwrite newer events, and clears nullable lastSeen and error on repeated observations.
• On an _acpmux/lagged notice, re-reads the snapshot so a peer that went down while the client lagged no longer shows as connected.
• This is the carrier foundation for draft #26796; remote-strip UI and real-machine validation remain outstanding, and native tests are included but unrun.