fix(tui): release stale daemon viewer leases

[lawrencecchen]

Stacked on #8460.

The durable daemon-side Admin connection used to remain a host viewer at its snapshot grid. After Chromium cut over from the compatibility control attachment to a direct renderer, the old Admin lease could keep the canonical terminal at 80x24 forever.

This PR:

• adds a red integration regression first, followed by the fix;
• auto-registers only resize-capable Renderer connections as snapshot viewers;
• explicitly releases Admin on every connect for compatibility with live protocol-v1 hosts from the parent branch;
• tracks the mux desired Admin lease across failed writes and replays it atomically during reconnect;
• propagates a missing effective mux viewer as ReleaseViewer;
• preserves smallest-viewer arbitration, same-size re-registration, and restores the direct renderer size after a TUI detaches.

Validation:

• regression repeated 20 times;
• terminal_host_recovery: 17 passed;
• cmux-tui-core: 223 unit + 44 integration/doc tests passed;
• cargo fmt --check and git diff --check passed.

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Summary by cubic

Fixes stale daemon viewer leases that could pin the PTY after switching to the direct renderer, and hardens zero‑width startup to avoid attach panics. Leases now release and re‑apply so the terminal follows the smallest active viewer; the sidebar stays hidden until a real size arrives.

• Bug Fixes
  • Only resize‑capable Renderer connections auto‑register as viewers; Admin and mirror clients never pin the grid.
  • On Admin connect, start from the snapshot and unconditionally release its lease (upgrades protocol‑v1 hosts).
  • Persist desired viewer size in the host across failed writes; replay atomically on reconnect/runtime swap and skip unchanged replays.
  • If a surface has no effective mux viewer, explicitly release the daemon mirror lease; re‑apply on the next viewer report and avoid redundant host reflows when sizes already match.
  • Preserve smallest‑viewer arbitration: the direct renderer becomes sole viewer after control disconnect, and its size restores after TUI detach; defer sidebar width clamp to tolerate zero‑width startup.

^{Written for commit 59dfa84. Summary will update on new commits.}

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Project	Deployment	Actions	Updated (UTC)
cmux	Ready	Preview, Comment	Jul 19, 2026 10:41am
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[lawrencecchen]

Superseded and landed cumulatively in #8717 (merge commit ea51d55). Closing this review-stack entry so the merged main branch is the canonical review surface.