Herdr FAQ

Launch and drive coding agents through Herdr (>= 0.9.0) without losing prompts.

Syntax authority

herdr --skill (~13k chars) is the vendor reference: command model, IDs, lifecycle states, prompt and wait mechanics, read sources, safety rules. Read it once per session before your first herdr command - this file assumes it and repeats none of it. For flags, run the command group bare (herdr agent, herdr pane) or --help; never bare herdr (it launches the TUI). If a syntax question is not answered here, it is answered there - go get it, never guess a flag.

When this lane

test "${HERDR_ENV:-}" = 1     # never drive herdr from outside a pane

Unset means this shell is not herdr-managed: no $HERDR_PANE_ID, no --current, and an untargeted command lands on whatever pane the USER has focused. Use acpx instead (acpx-faq). In-session fan-out stays on the harness's own subagent tool.

Invariants

1. Exit 0 is submission, never completion - and send-keys can return {"type":"ok"} for keystrokes that never reach the pane. Confirm by effect: state moved, or the text is visible in the pane.
2. Screens no detection rule matches read as idle. agy has no idle rule at all, so every agy idle is a guess. Read the screen before the first prompt, always.
3. agent start timeout = the child never launched (bad flag, PATH, or a wrapper process). pane read has the real error; pane process-info and herdr's own message do not.
4. idle is not "finished". A claude turn that spawned background shells or a background MCP task ends and reports idle while that work runs on; --wait tracks lifecycle state, not turns.
5. The driving harness is a second gate. Dangerous passthrough flags (--dangerously-*, danger-full-access) get classifier-blocked, and so can ordinary brief content inlined into a shell command. sleep N; herdr ... polling is banned - use one backgrounded prompt, or wait on a file.

Per kind

Model defaults unless the task argues otherwise: codex gpt-5.6-sol at reasoning_effort high (set via codex's own flags/config - check codex --help), claude claude-opus-5, agy gemini-3.7-flash-medium (measured on par with Opus for rubric-driven bulk work and far faster; gemini-3.8-flash-high measured worse on the same task). One directory per agent, always.

codex

P=$(herdr pane split --current --direction right --cwd "$D" --no-focus | jq -r .result.pane.pane_id)
herdr agent start cx1 --kind codex --pane "$P" --timeout 90000 -- --approve-for-me --no-alt-screen
herdr agent read cx1 --source detection --lines 40        # ALWAYS, before the first prompt
herdr agent prompt cx1 "Carry out $D/brief.md." --wait --timeout 1800000 &

Never --full-auto: removed in 0.15x, it surfaces as a bare timeout and can wedge the pane in startup-pending. The trust-directory and startup-update dialogs are detected, so an untrusted dir fails fast with agent_not_ready rather than eating the first prompt. The one-time post-integration install hooks-review gate is NOT detected (WONTFIX) - answer it once per machine. Session ref binds at the first prompt for a fresh start; an explicit -- resume <id> is persisted at launch.

claude (alias claude-code)

# Pre-trust first - the folder-trust dialog IS detected, so an untrusted dir fails the
# start. Trust is INHERITED: a new dir under an already-trusted parent needs nothing.
CFG=/tmp/agentcfg; mkdir -p "$CFG"                        # isolated from your real config
printf '{"projects":{"%s":{"hasTrustDialogAccepted":true}}}' "$D" > "$CFG/.claude.json"

P=$(herdr pane split --current --cwd "$D" --no-focus --env CLAUDE_CONFIG_DIR="$CFG" \
    | jq -r .result.pane.pane_id)
herdr agent start cl1 --kind claude --pane "$P" --timeout 90000 -- --model claude-opus-5
herdr agent read cl1 --source detection --lines 40        # ALWAYS, before the first prompt
herdr agent prompt cl1 "Carry out $D/brief.md." --wait --timeout 1800000 &

• The safe key differs per dialog. The folder-trust dialog puts the cursor on No, exit, so a bare enter kills the agent - send down enter. The Bash-permission dialog puts the cursor on 1. Yes.
• idle lies in a specific way here. Background shells end the turn and report idle while they run; background agents and MCP tasks keep it working, and a background MCP task can hold idle for its whole 3-10 minute life.
• Grey next-prompt-suggestion text reads as real unsubmitted text in a plain read - disambiguate with --format ansi (the suggestion carries the dim attribute ESC[2m).
• Session ref binds at launch. A Claude Code UI update can break detection (herdr server update-agent-manifests). Native-launcher installs run under a version-string process herdr cannot identify: launch via HERDR_AGENT=claude exec <path>, then agent rename.
• Under a different CLAUDE_CONFIG_DIR the agent loads its own skills. Confirm they are current before its first turn - a running session has already snapshotted the old text.

agy (aliases antigravity, antigravity-cli)

Thinnest detection of the three: no idle rule at all (invariant 2), and nothing in the pre-flight is recoverable once the agent is up.

D=/abs/dir/for/this/agent                   # ONE dir per agent - agy reads sibling files
mkdir -p "$D"; : > "$D/report.md"           # pre-create the output file

python3 - "$D" <<'PY'                       # pre-trust; the dialog is unanswerable (below)
import json, pathlib, sys
p = pathlib.Path.home() / ".gemini/antigravity-cli/settings.json"
d = json.loads(p.read_text()) if p.exists() else {}
tw = d.setdefault("trustedWorkspaces", [])  # a list of exact paths, not a map
if sys.argv[1] not in tw: tw.append(sys.argv[1])
p.write_text(json.dumps(d, indent=2) + "\n")
PY

P=$(herdr tab create --workspace "$WS" --cwd "$D" --label ag1 --no-focus \
    | jq -r .result.root_pane.pane_id)      # one TAB per agent, never N panes in one tab
herdr agent start ag1 --kind agy --pane "$P" --timeout 120000 \
  -- --model gemini-3.7-flash-medium --effort medium --mode accept-edits
herdr agent read ag1 --source detection --lines 15   # read the banner, not the status
herdr agent prompt ag1 "Carry out $D/brief.md. Write your report to $D/report.md." \
  --wait --timeout 1800000 &                # then poll for the file, not the state

• The trust dialog is unanswerable from this side. agent start returns idle, the screen holds Do you trust the contents of this project?, and send-keys enter no-ops against it - repeatedly, silently, exit 0. --dangerously-skip-permissions is classifier-blocked before it reaches herdr (invariant 5). Only a config entry written before agent start pre-empts it.
• Trust lives in trustedWorkspaces in ~/.gemini/antigravity-cli/settings.json, NOT ~/.gemini/trustedFolders.json (the Gemini CLI's file - observed ignored on agy 1.2.0). Pre-writing it is not confirmed end to end, and a harness classifier may refuse the edit as a trust-config change - when it does, drive agy through acpx instead (acpx-faq): its ACP server has no folder-trust dialog.
• One tab per agent. Four agy panes in one tab leaves ~29 columns: the TUI stops rendering, input races swallow prompts, and detection sees only the pane's own rows, so the state you read is wrong too.
• Read the startup banner before blaming herdr. <account> (Google AI Pro) means entitlement is reaching Code Assist. A bare address, or Eligibility check failed: UNAVAILABLE (code 503), means dead on arrival however healthy the status looks - re-auth, do not re-prompt.
• not a valid artifact path is agy-internal, not your filesystem. ArtifactMetadata on a write_to_file confines the write to ~/.gemini/antigravity-cli/brain/<session-id>/. It self-recovers by retrying as Edit; pre-creating the file empty skips the round trip.
• agy reads sibling files unprompted - agents sharing a directory reproduce each other's output. Own directory each, and md5 any rerun before believing an agreement number: byte-identical multi-KB prose is copying, not consensus.
• Premature done lasts up to ~50s mid-turn while the pane visibly streams - wait on the report file, never a settled state. A first prompt can be swallowed entirely with agent_prompt_stalled and no trace in the composer; re-prompt, never send-keys. No session ref until the first prompt. Integration install target is antigravity-cli; ~/.gemini/config must exist (or ANTIGRAVITY_CLI_CONFIG_DIR).

Integrations for all three are session-restore only - they never improve state detection - and their hooks silently no-op without python3 on PATH. integration status cannot see a codex-side disabled hook (WONTFIX); verify agent_session is present after the first codex turn instead.

Launch and fleets

• Fleets: one tab per agent (herdr tab create --workspace "$WS" --cwd "$D" --no-focus), own workspace, --no-focus everywhere. Repeated splits leave panes narrow, and a TUI below its minimum width stops rendering, swallows input, and hides its state from detection (which sees only the pane's own rows; fallback 24).
• Always agent read --source detection before the first prompt (invariant 2) and branch on it - never blind-fire a key at a dialog. After answering one, gate on agent wait <n> --until idle done --timeout 60000: a bare wait returns the still-blocked state within milliseconds, a no-op that looks like the key never landed.
• Names die with the agent and freed names get recycled - namespace them (myproj-reviewer). After a killed agent start, one herdr agent get <name> frees the reservation (reconciliation is lazy). An agent TARGET can be a bare pane id (agent prompt w1K:p1 '<text>') - how you reach an unnamed agent without renaming someone else's.
• Test -n "$P" after capturing a pane id: an empty one makes later parsers blame the wrong token.

Composing traps

• agent read and pane read return raw pane text; the other agent/pane/workspace commands return JSON. Piping raw text to jq dies with parse error: Invalid numeric literal and you silently lose the read - use tail, grep -qF.
• pane read <id> takes the pane positionally and has no --pane at all (unknown option: --pane); pane close likewise. When in doubt read the Usage: line - it names positionals in angle brackets.
• agent start --timeout defaults to 30000 and caps at 300000. agent prompt --timeout has no cap (1800000 is fine) but is rejected with --timeout requires --wait when --wait is absent - and backgrounded, that failure is invisible and the prompt is never written. Fire-and-forget sends take no flags.
• agent list JSON is sparse: name is absent (not null) for unnamed agents, and a pending start is {"agent_status":"unknown","launch_pending":true}. Null-guard every string op: select((.name // "") | startswith("myproj-")).
• Env vars go in --env KEY=VALUE at pane/tab/workspace creation, never pane run 'export ...' (a subshell the agent never sees). Repeated flags go inline - zsh does not word-split an unquoted $E, so E="--env A=1 --env B=2" arrives as one bogus argument.
• Bad flags print usage partly on stdout, so a | jq pipeline turns it into a misleading parse error - check exit status before parsing.

Drive

• Wait on the artifact, not the state. End every non-trivial brief with "write your full report to <path> and reply with only the path", and poll for the file. idle arrives on interrupted turns, on fleet parents that dispatched children, and for the whole life of a claude background MCP task (invariant 4) - a watcher on != working false-alarms on every one of those.
• Gate decisions on agent_status, never interactive_ready (it stays true while blocked).
• Long text is safe through agent prompt (bracketed paste; 8 KB arrives intact); the 1024-byte macOS tty truncation applies to pane send-text and keystrokes. Pass file paths anyway - it also keeps brief content out of the shell command (invariant 5).
• Queue follow-ups behind a working agent freely (prompt refuses blocked agents before writing anything) - but no --wait on a queued follow-up: it can be satisfied by the turn already running.
• Slash commands that open dialogs trip the fixed 5s stall gate - verify those by screen read, not --wait.
• Exit: confirm positively - pane process-info shows the shell back in the foreground - then pane close. Never regex the prompt.

Failures

Triage first:

• Any start failure -> herdr pane read <pane> --source visible FIRST. Most common: the child launched, printed error: unknown option ..., and exited - process-info looks innocent and herdr reports a bare timeout. Then process-info: a foreign foreground process = busy/race; an agent under a wrapper (node, a bare version string) = relaunch via HERDR_AGENT=<kind> exec <cmd>, then agent rename; under docker exec, podman exec, or ssh -t = permanently undetectable (WONTFIX).
• Any wrong state -> agent explain <target> --verbose + agent read --source detection. Matched rule null + default_known_agent_idle_fallback = herdr is guessing. Stale manifest -> herdr server update-agent-manifests (no restart). Local rule patch: ~/.config/herdr/agent-detection/<kind>.toml. Logs: ~/.config/herdr/herdr-server.log, HERDR_LOG=herdr=debug.
• After a binary update, do NOT reflexively server stop - it kills every pane process and in-flight turn, unresumably. 0.9.0 leaves a compatible server and its agents untouched; trust herdr status (endpoint_compatible, restart_needed, server_binary_stale). A stale CLIENT inverts the picture: it calls the server "old" while pane list correctly says client protocol N is older than server.
• "herdr is stuck" is often the terminal emulator, not herdr - open a fresh tab before touching the server.

Catalog:

• agent_not_ready (start) - a dialog is on screen; exit 1 but the agent is running and the name is bound. Read, answer via send-keys (safe keys in Per kind), gate --until idle done, prompt. A blocked launch never times out (launch_pending stays true until answered). agy's trust dialog is NOT detected and reads as idle instead - see agy.

• timeout (start) - invariant 3; read the pane. command not found in a non-login shell: set [terminal] shell_mode = "login", recreate the pane. Under --remote, panes inherit the SERVER's PATH, so a ~/.local/bin agent CLI gives a bare timeout.

• agent_name_taken / agent_launch_pending - reservations reconcile lazily: one herdr agent get <name> frees an expired one. Still wedged: burn both - fresh pane, fresh name.

• agent_pane_busy - "available shell" = the shell itself, alone, in the foreground. (a) racy rc files (starship, direnv): herdr retries only 2s and pane get looks identical ready vs not - retry with backoff, clean up orphaned tabs; (b) genuine occupant: split a new pane, never reclaim (killing the occupant cascades into pane_not_found). (Windows: pwsh chain-launch profiles nest shells - set [terminal] default_shell = "pwsh.exe".)

• agent_not_found - downstream symptom: failed start, exited agent, or a bad name earlier in the loop. A live pane can rarely lose registration while the TUI runs fine - agent rename <pane> <same-name> restores it.

• timeout (prompt --wait / wait) - usually the turn outlasted the timeout: agent get shows working. Use 1800000+, background it, never resend on timeout alone.

• agent_prompt_stalled - not proof of non-delivery; the text may have landed and been consumed. Causes in observed order: stale manifest; a dialog-opening prompt; a target-side paste modal swallowing Enter (omp's Large Paste Menu triggers on line count, not bytes - disable it in omp /settings). Never blind-resend and never recover with a lone send-keys enter. Read the pane, then re-send with a fresh agent prompt:

  for i in 1 2 3; do
    herdr agent prompt "$A" "$TEXT" --wait --timeout 60000 && break
    herdr agent read "$A" --source recent-unwrapped --lines 200 | grep -qF "${TEXT:0:80}" && break
  done
  

• agent_blocked (prompt) - refused before anything is written. Read detection, surface the dialog, answer via send-keys.

• invalid_agent_name - [a-z][a-z0-9_-]{0,31}; uppercase from shell loops cascades into a wall of agent_not_founds.

• pane_not_found / workspace_not_found / unknown option: <valid-looking value> - IDs are runtime-only, never reused: re-list at session start, recreate only what is missing. unknown option on a whole flag string is the zsh variable trap (see Composing traps); on a lone token it is usually an empty $P.

• workspace_group_close_required - closing a primary workspace with open worktree workspaces needs workspace close --group; tab close can likewise return confirmation_required for a worktree group.

• Harness blocks - classifier denial on dangerous passthrough flags: put permissiveness in the child agent's own config ("Stage 2 classifier error" is transient - retry once). Allowlist the read-only commands (agent get/read/list/wait/explain, pane read/list/process-info, workspace list) or every call prompts.

Silent failures (exit 0, no error): fallback-idle prompt swallowing (invariant 2); send-keys returning ok without delivering; a bare agent prompt leaving text unsubmitted in an out-of-view pane; a first turn going straight unknown -> working -> idle skips done and its notification; a tall dialog partly invisible in a short pane (detection sees only the pane's own rows); pane wait-output matching the echoed command itself - never use it for readiness; agent focus returning ok without moving the viewport in 0.9.0 - use tab focus.