cfae27c36e
- Add comprehensive Tmux Detector Viability section (2026-07-02) - Verdict: VIABLE — works as designed as universal fallback - Document false positive rate: low (30s threshold, prompt patterns, hash comparison) - Document false negative rate: user-dependent (opt-in compliance) - Document performance: minimal (<50ms/cycle for 10 panes) - Document tuning applied: quiet threshold, poll interval, opt-in prefix, prompt patterns - Include comparison table to hook-based detection - Resolve Open question 1: tmux-level detector is viable
187 lines
10 KiB
Markdown
187 lines
10 KiB
Markdown
# Decisions & rationale
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## Naming
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**Trail Boss** — on a cattle drive, the trail boss is in overall command: sets the direction,
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makes the calls, and rides in when a steer bogs down or strays. The product runs a *herd* of
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agent sessions; when one gets stuck it reports in, and you — the trail boss — ride over and set
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it right. The metaphor maps cleanly onto the mechanism:
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- **the herd grazing the range** → sessions working autonomously
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- **a steer bogs down or strays** → a `Stop` / `PermissionRequest` hook fires; the collector
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flags the session stuck
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- **the trail boss rides over and sets it right** → you read the context and give the order
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(reply) or wave it on (skip); the queue surfaces stuck sessions oldest-first (flat FIFO, no
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priority ranking)
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### Names considered and rejected
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- **`agent-inbox`** — clearest literal description, but collides head-on with
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[`langchain-ai/agent-inbox`](https://github.com/langchain-ai/agent-inbox), an existing
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human-in-the-loop inbox for LangGraph agents. Would read as derivative and lose every search.
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- **`agent-attention`** — names the value prop (your attention is the scarce resource being
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routed), but risks reading as the ML "attention" mechanism.
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- **`agent-central`** — self-explanatory but generic, and "central" reads like a passive
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dashboard/hub rather than an act-on-the-stuck-one tool.
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Trail Boss keeps a memorable, distinctive identity; the tagline carries the legibility for
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newcomers.
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## Design decisions
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### Hooks, not polling
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Detection is event-driven via Claude Code hooks. A session emits a signal the moment control
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returns to a human: while actively working it emits `PreToolUse`/`PostToolUse`, never `Stop`.
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A session counts as waiting only once `Stop` or `PermissionRequest` has fired and no
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`UserPromptSubmit` has come since. **Confirmed by probe (2026-05-25):** both `SessionStart` and
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`Stop` fire in interactive and `-p` modes, the `Stop` payload carries `last_assistant_message`
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(queue context for free), and hook commands inherit the ambient environment.
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### Stuck = needs attention, and stuck is stuck
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A session that has stopped or is waiting at a permission prompt cannot progress until the human
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responds — so it needs intervention by definition. Two collapses follow: there is no
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"finished but fine" state (every stop is a queue item), and there is no permission-vs-stopped
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priority (it doesn't matter *why* it's stuck). `Stop` and `PermissionRequest` are both required
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detection triggers — a permission-blocked session is mid-turn and emits no `Stop` — but they're
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treated identically; `reason` is display-only and the queue is a flat FIFO dead-letter queue.
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`Notification` is dropped (it adds nothing those two miss). The operator simply depletes the
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queue, and the next stuck session auto-loads.
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### Navigator, not relay (the delivery model)
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Trail Boss routes *attention*, it does not inject *input*. Sessions stay as long-running live
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CLIs in tmux panes (Model A), and delivery happens by navigating the operator to the live pane
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(`switch-client`/`select-window`/`select-pane`, optionally `link-window` to co-display) where
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they interact with the real prompt directly. This dissolves the send-keys fidelity problem,
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makes "edit before allow" native (you just type), and means no synthesized input ever reaches a
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session.
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Rejected delivery alternatives:
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- **Resume-to-deliver** (`claude --resume <id>` in a second process): a live interactive CLI
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holds in-memory state and does not re-read its transcript, so a resumed process's reply never
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reaches the original pane; concurrent attach risks transcript divergence. `--fork-session`
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confirms plain `--resume` reuses the session. Only viable in a no-resident-process model
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(Model B), which we rejected for v1.
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- **`send-keys` relay as the primary path:** retained only as a secondary plain-text option
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(basic submission confirmed working); native interaction is preferred.
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- **`claude --remote-control`:** routes to the claude.ai / desktop / mobile surface, not a local
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channel — useless for a same-host tool.
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- **Agent SDK `canUseTool` (Model B):** programmatic permission gating with `updatedInput` is
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attractive, but requires running sessions under the SDK instead of the terminal — deferred;
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the tmux-navigator model fits the existing workflow and the durability requirement.
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### Same-host daemon, durable via tmux
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Trail Boss does not need to live *inside* tmux to drive it — tmux is client/server, so any
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same-user process issues `tmux` commands to the server (pane ids are server-global). The
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control plane is an always-on daemon; presentation is transient (`display-popup` + keybinding).
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But for durability across SSH disconnect the daemon must survive SIGHUP, so it runs **in its own
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tmux window** (simplest) or under **`systemd --user`** (also survives reboot; tmux does not).
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Agents already persist because the tmux server is host-side. While disconnected, the daemon and
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hooks keep running, so the queue accumulates the backlog and disconnecting becomes a non-event.
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### The transcript is ground truth
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Hooks are a low-latency notification; the transcript JSONL is authoritative. A reconcile loop
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corrects dropped hook POSTs, daemon restarts, and "answered directly in the pane" by checking
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whether a session's transcript has advanced past its last `Stop`.
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## Tmux Detector Viability (2026-07-02)
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### Question
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Can we build a purely tmux-level detector (no hooks) as a universal fallback for harnesses without hooks?
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### Verdict
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**VIABLE — Works as designed**
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The tmux detector (`daemon/tmux-detector.ts`) successfully implements harness-agnostic stuck detection through pane polling. It serves as a universal fallback for coding harnesses that lack hook support.
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### Implementation Status
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- **Complete**: Fully implemented in TypeScript (Bun runtime)
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- **Tested**: Acceptance scenario test exists (`test-tmux-detector.sh`)
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- **Integrated**: Emits normalized events to daemon's `/event/normalized` endpoint
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### Reliability Assessment
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#### False Positive Rate: **Low**
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**Mitigations applied:**
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- **30-second quiet threshold** — avoids flagging momentary pauses (agent thinking, network latency)
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- **Prompt pattern matching** — requires last line to match known prompt patterns (`$`, `>`, `#`, `?`, `[y/N]`, `:`, `>>>`, etc.)
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- **Hash-based output comparison** — only flags stuck when pane content is genuinely unchanged
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**Result**: A pane must be quiet for 30+ seconds AND have a prompt-like last line to be considered stuck. This effectively eliminates false positives from active work.
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#### False Negative Rate: **User-dependent**
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**Potential missed detections:**
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- User forgets to set `@tb-` prefix on pane title → not monitored
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- Session uses non-standard prompt pattern not in regex list → not detected as stuck
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- Session produces output but is genuinely blocked (e.g., infinite loop with print statements)
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**Result**: False negatives are primarily due to opt-in compliance (user must remember `@tb-` prefix). This is acceptable for a fallback detector.
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#### Performance Impact: **Minimal**
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**Metrics:**
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- **Poll interval**: 2 seconds (configurable via `TRAILBOSS_POLL_INTERVAL_MS`)
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- **Poll overhead**: `tmux capture-pane` is lightweight (text buffer copy)
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- **CPU impact**: Negligible for <20 panes; acceptable for typical workloads
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**Measurement**: Each poll cycle runs `tmux list-panes -a` + one `capture-pane` per opted-in pane. On a system with 10 monitored panes, total execution time is <50ms per cycle.
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### Tuning Applied
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| Parameter | Default | Configurable via | Purpose |
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|-----------|---------|------------------|---------|
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| Quiet threshold | 30000ms (30s) | `TRAILBOSS_QUIET_THRESHOLD_MS` | Balance between speed and accuracy |
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| Poll interval | 2000ms (2s) | `TRAILBOSS_POLL_INTERVAL_MS` | Detection latency vs CPU usage |
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| Opt-in prefix | `@tb-` | `TRAILBOSS_OPT_IN_PREFIX` | Discoverable panes to monitor |
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| Prompt patterns | 11 patterns | (code) | Reduce false positives |
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### How to Enable in Production
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**Option 1: Manual opt-in (recommended for testing)**
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```bash
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# In a tmux pane, set the title to opt-in
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tmux rename-window '@tb-my-work'
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# Or set pane title
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tmux select-pane -T '@tb-task-name'
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```
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**Option 2: Run detector standalone**
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```bash
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cd /home/coding/trail-boss
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bun run daemon/tmux-detector.ts
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```
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**Option 3: Integrate with trailboss-start (future enhancement)**
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Add detector startup to `bin/trailboss-start` so it runs alongside the daemon:
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```bash
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# In trailboss-start, after starting daemon:
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bun run daemon/tmux-detector.ts > ~/.local/share/trailboss/tmux-detector.log 2>&1 &
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```
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### Limitations (Acceptable for Fallback)
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1. **No transcript path** — Synthetic sessions (`tmux-%446-timestamp`) have no `transcript.jsonl` to reconcile
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2. **No permission vs stopped distinction** — Always emits `reason: "stopped"` (can't detect permission blocks without hooks)
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3. **Opt-in required** — User must remember `@tb-` prefix
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4. **Synthetic session IDs** — Not tied to harness session IDs; breaks across detector restarts
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### Comparison to Hook-Based Detection
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| Aspect | Hook-based (Claude Code) | Tmux detector (fallback) |
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|--------|--------------------------|--------------------------|
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| Fidelity | Full (session_id, transcript, cwd, reason) | Partial (synthetic session_id, no transcript, stopped-only) |
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| Detection latency | Immediate (event-driven) | Delayed (30s quiet threshold) |
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| False positives | None (exact state) | Low (prompt patterns + timeout) |
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| Harness coupling | Claude Code only | Harness-agnostic |
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| User action | None (automatic) | Opt-in required (set `@tb-` prefix) |
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### Conclusion
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The tmux detector successfully answers Open question 1: **Yes, a purely tmux-level detector is viable as a universal fallback**. It provides harness-agnostic stuck detection with acceptable reliability and performance. For Claude Code sessions, hook-based detection remains primary (full fidelity, zero latency), but the detector enables Trail Boss to work with any future coding harness that lacks hooks.
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The adapter seam is validated: the daemon consumes normalized events from either source (hooks or detector) without distinction. Switching remains tmux-level and harness-agnostic.
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