VUH-1867: hand-started Claude channel startup fix

James authorized automatic channel setup if supported, otherwise a one-step startup fix, with live proof in an owned throwaway Mac pane. The implementing lead chose the fallback after reading the official channel controls: users must opt a server into each session with --channels; installation and managed channelsEnabled/allowedChannelPlugins only make it available. The SessionStart hook supplies context and user-visible JSON systemMessage, not changes to launch argv. CLAUDE_ENV_FILE sets environment for later Bash commands, not the already selected session channel. No supported plugin-only automatic opt-in was found.

The hook now shows:

Clankie's live messages are off in this pane. Restart this session with:
claude --resume SESSION_UUID --channels plugin:clankie-worker@clankie

It uses a validated native UUID and the matching fleet descriptor. The warning runs before the lifecycle HTTP report, so a refused report cannot suppress it. Process ancestry handles intermediary command shells; unavailable ancestry uses “cannot confirm” wording. Exact normal/development plugin opt-in suppresses the warning. Development opt-in still requires Claude's interactive native confirmation and organization policy; the hook does not bypass either.

Checks

Sixteen real command-hook subprocess cases use an actual intermediary shell, recorded native argv, a private Herdr socket fixture and a loopback lifecycle listener. They cover exact resume output, normal/equals/multiple/development flags, different plugins, refused reporting, unlinked/missing/ambiguous panes, non-startup/Codex/print contexts, unsafe IDs and unavailable launch observation. The existing three permission command-hook cases also pass (19 tests across the two files). The five-file test:seat-delivery gate passes all 86 tests, including exact/lost/missing-ID/wrong-ID ACK cases with the shared launch parser. The heavy TUI typecheck and scoped formatting, lint and documentation link checks pass. No repository-wide suite, eval or deployment ran.

Native Mac proof

At 02:58:21 UTC on 2026-10-09, Claude Code 2.1.295 in the owned throwaway pane w47:pG displayed:

SessionStart:startup says: Clankie's live messages are off in this pane.
Restart this session with: claude --resume 3c343503-c3fc-4074-9fd6-5250b471d51b --channels plugin:clankie-worker@clankie

The native process had no channel flag. Instrumentation selected the checkout SessionStart hook and explicit session UUID through a temporary settings file, with an isolated loopback lifecycle listener. The actual hook reported that same session before proof was captured. No prompt or brief was typed or sent. This proves the live user-visible startup fallback, not a deployed installed plugin or Windows execution. The own child was stopped afterward, releasing its heavy permit. Raw ignored evidence is in .local/claude-proof/startup-runtime/ (evidence.jsonl, native-startup.txt, debug.log).

PC live execution remains untested under James's explicit Mac-only proof and no-PC-input boundaries. Existing panes, dotfiles and the installed captain were untouched. The channel wake behavior itself has separate owned native proof in VUH-1870 and VUH-1868.