refactor: remove unused cross-agent-comms subsystem

Nothing used the cross-agent message system (send/recv/watch/status/discover/halt/resume over the inbox/from-agents/ file-IPC protocol). Every cross-project handoff goes through inbox-send instead. I removed the scripts, READMEs, workflow, tests, INDEX entry, the three startup.org wirings, and the legacy bin symlinks, then repointed helper-mode's escalation to inbox-send and noted the removal in the generic-agent-runtime spec.

1 files changed, 0 insertions, 134 deletions

diff --git a/.ai/scripts/cross-agent-comms/cross-agent-halt.md b/.ai/scripts/cross-agent-comms/cross-agent-halt.md
deleted file mode 100644
index b817fbc..0000000
--- a/.ai/scripts/cross-agent-comms/cross-agent-halt.md
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-# cross-agent-halt
-
-**Purpose.** Failsafe stop for all cross-agent activity on the local machine
-(or, with `--tailnet`, across all configured peers). Creates the HALT file
-that every component in the protocol checks; within one polling cadence
-(~5 min) all polling, sending, watching, and receiving stops.
-
-This is the user's emergency brake. Use when something is misbehaving and
-visiting individual sessions is too slow.
-
-## Usage
-
-```
-cross-agent-halt [reason] [--tailnet] [--no-stop-watcher]
-```
-
-### Positional argument
-
-| Position | Meaning | Example |
-|---|---|---|
-| 1 | Optional human-readable reason for the halt. Written into the HALT file's body. Helps future-you remember why you stopped things. | `"investigating runaway poll loop, 2026-04-27"` |
-
-### Flags
-
-| Flag | Default | Purpose |
-|---|---|---|
-| `--tailnet` | local only | Propagate halt to every peer in `peers.toml` via SSH over Tailscale. |
-| `--no-stop-watcher` | (stops watcher) | Skip stopping the `cross-agent-watch.path` systemd unit. Useful if the watcher is intentionally separate from comms (rare). |
-
-## Behavior
-
-### Local halt (default)
-
-1. Write the HALT file: `~/.config/cross-agent-comms/HALT`. If a `[reason]` was
-   passed, write it as the file's body. Otherwise the file is empty (existence
-   alone triggers halt).
-2. Stop the watcher service: `systemctl --user stop cross-agent-watch.path`
-   (and the corresponding `.service` if running).
-3. Print a summary:
-   ```
-   ✓ HALT file written: ~/.config/cross-agent-comms/HALT
-   ✓ Watcher service stopped (cross-agent-watch.path)
-   - In-flight sends will complete their current rsync step (~seconds), then
-     stop. New sends are blocked.
-   - Active agent polling sessions stop within one cadence (~5 min).
-   - Use `cross-agent-resume` to clear HALT.
-     Per-session polling does NOT auto-resume — you re-engage each session by
-     telling its agent to resume polling.
-   ```
-4. Exit 0.
-
-### Cross-tailnet halt (`--tailnet`)
-
-1. Apply local halt steps 1-2 first.
-2. Read `peers.toml` for the list of remote machines.
-3. For each peer, SSH and write the HALT file:
-   ```
-   ssh <user>@<host> "echo '<reason>' > ~/.config/cross-agent-comms/HALT && \
-                       systemctl --user stop cross-agent-watch.path"
-   ```
-4. Track per-peer success/failure. Print results:
-   ```
-   Halting velox.local       ✓ (HALT file written)
-   Halting bastion.local     ✗ (ssh exit 255: no route to host)
-   Halting locally           ✓ (HALT file written)
-
-   PARTIAL HALT: 2/3 machines halted. bastion.local needs manual halt.
-   ```
-5. Exit 0 if all peers halted; exit 1 if any peer failed (so scripts can
-   detect partial halt). The local halt always succeeds — even on `--tailnet`,
-   if remote peers fail, local is still halted.
-
-## What "halt active" means for each component
-
-| Component | Behavior under HALT |
-|---|---|
-| `cross-agent-send` | Refuses to send. Exits 5 with "halt active; remove ~/.config/cross-agent-comms/HALT to resume." Checks HALT at start AND between each retry/rsync step, so an in-flight send completes its current step then stops. |
-| `cross-agent-recv` | Refuses to verify or dedup. Exits 5 with same message. Inbound files are **left in place** — not moved, not rejected — so resume picks them up cleanly via cold-start. |
-| `cross-agent-watch` | Continues running but suppresses notifications. Logs each event with `(suppressed by HALT)` so the operator can see what would have fired. |
-| `cross-agent-status` | Prints prominent `⚠ HALT ACTIVE` banner before normal output. Continues to enumerate (read-only). |
-| `cross-agent-discover` | Same banner. Continues (read-only). |
-| Agent polling loops | Check HALT on every wake. If set: write a final `progress` note to any active conversation ("HALT fired locally; pausing"), surface "(HALT active; cross-agent comms paused)" in every user response, and stop rescheduling. Polling decays naturally within one cadence. |
-| Conversation initiator | Refuses to write sequence 1 of any new conversation. Surfaces refusal to user. |
-| Startup workflow (Phase A) | Checks HALT at session boot. If set, surfaces immediately and skips cross-agent inbox checks. |
-
-## Failure modes
-
-| Symptom | Cause | Fix |
-|---|---|---|
-| `~/.config/cross-agent-comms/HALT` already exists | Halt was already active | OK — running halt again refreshes the reason text. Safe. |
-| `systemctl --user stop` fails | Watcher service not installed, or systemd not available | The HALT file is still written — components that check HALT will still stop. The systemctl failure surfaces as a non-fatal warning. |
-| `--tailnet` halts some peers but not others | One or more peers unreachable | Exit 1 with per-peer status. Manually halt the unreachable peers (visit each machine, `touch ~/.config/cross-agent-comms/HALT`), or fix the network and re-run. |
-| Permission denied writing the HALT file | `~/.config/cross-agent-comms/` doesn't exist or is owned by another user | `mkdir -p ~/.config/cross-agent-comms/`; check ownership. |
-
-## What halt does NOT do
-
-- Does not kill running Claude sessions. Polling stops within ~5 min, but the
-  session itself stays alive and can be re-engaged after resume.
-- Does not delete pending messages. Inbound files in `inbox/from-agents/`
-  remain; they get processed when polling resumes.
-- Does not abort in-flight rsync push mid-byte. Atomic-write semantics
-  guarantee in-flight messages either complete cleanly or leave only `.tmp.*`
-  files (which receivers ignore).
-
-## Examples
-
-```bash
-# Quick halt with no reason
-cross-agent-halt
-
-# Halt with a memo
-cross-agent-halt "runaway poll loop in homelab session, debugging"
-
-# Halt all tailnet peers + local
-cross-agent-halt --tailnet "shutting down for system update"
-
-# Halt protocol comms but leave the watcher service running
-cross-agent-halt --no-stop-watcher
-```
-
-## Recovery
-
-Always pair with `cross-agent-resume` when the situation is resolved:
-
-```bash
-cross-agent-resume                # local
-cross-agent-resume --tailnet      # all peers
-```
-
-## See also
-
-- `cross-agent-resume` — counterpart that clears HALT.
-- `cross-agent-status` — see HALT state at a glance.
-- `cross-agent-comms.org` — protocol spec, `* Halt mechanism` section.