hooklib: router + nix-deploy-output PreToolUse hook
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oleks
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{
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"name": "hooklib",
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"version": "0.1.0",
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"description": "A library of small, composable Claude Code hooks. Each hook is a drop-in script under hooks/<event>.d/ dispatched by a shared router. Ships with nix-deploy-output: a PreToolUse guard that rewrites/blocks bare `nix run .#deploy` (deploy-rs) invocations so their build/activation logs actually show up in Claude Code instead of rendering as empty output — it requires the command force plain, line-buffered logs via `2>&1 | cat`.",
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"author": {
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"name": "oleks",
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"email": "plugins@oleks.space"
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},
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"license": "MIT",
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"keywords": [
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"hooks",
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"pretooluse",
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"nix",
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"deploy-rs",
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"bash",
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"output",
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"guardrail"
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]
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}
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.cache/
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.claude/
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*.log
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# hooklib
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A small **library of composable Claude Code hooks**. Each hook is a drop-in
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script; a shared router dispatches one event to all of them. Adding a hook is
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just dropping an executable script into the matching directory — no wiring.
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## Layout
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```
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hooks/
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hooks.json # registers the router per event (currently PreToolUse:Bash)
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dispatch.sh # router: feeds the event JSON to every hooks/<event>.d/*.sh
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pretooluse.d/
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10-nix-deploy-output.sh
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```
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### How dispatch works
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`dispatch.sh <Event>` reads the event JSON from stdin once and replays it to
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each script in `hooks/<event>.d/` (lexical order). A sub-hook that wants to act
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prints a hook JSON response to stdout and exits 0; the **first** sub-hook to
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emit non-empty output wins and the router forwards it verbatim. If nobody
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speaks up, the router is silent (Claude Code treats that as "allow").
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Scripts are numbered (`10-`, `20-`, …) to make ordering explicit.
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## Hooks
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### `nix-deploy-output` (PreToolUse / Bash)
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**Problem:** `nix run .#deploy` (deploy-rs) shows **empty output** in Claude
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Code. deploy-rs and nix render progress as an ANSI spinner on a TTY and log to
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stderr; captured non-interactively, that collapses to a blank.
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**Fix:** the command must fold stderr into stdout and defeat TTY detection so
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the tools emit plain, line-buffered logs. The canonical form is:
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```
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nix run .#deploy 2>&1 | cat
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```
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The hook inspects any `nix run .#deploy…` command. If it is already in the
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output-safe form (`2>&1` **and** a pipe into `cat`/`tee`/`less`) it passes
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through untouched. Otherwise it **denies** the call and returns the corrected
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command (preserving any `--` flags / host target) for Claude to run instead.
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## Adding another hook
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Drop `hooks/<event>.d/NN-name.sh` (executable) that reads the event JSON on
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stdin and prints a hook response only when it wants to intervene. If the event
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isn't `PreToolUse`, add it to `hooks/hooks.json` pointing at
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`dispatch.sh <Event>`.
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## Install (local dev)
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```
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claude plugin install hooklib@oleks-local
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```
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Executable
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#!/usr/bin/env bash
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# hooklib dispatcher — routes one Claude Code hook event to every drop-in
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# script under hooks/<event>.d/, in lexical order.
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#
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# Usage (from hooks.json): dispatch.sh <EventName>
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#
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# The event JSON is read once from stdin and replayed to each sub-hook on
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# its own stdin. A sub-hook that wants to act prints a hook JSON response
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# (e.g. a PreToolUse permissionDecision) to stdout and exits 0. The FIRST
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# sub-hook to emit non-empty stdout wins: the dispatcher forwards that
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# response verbatim and stops. If no sub-hook emits anything, the dispatcher
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# stays silent and exits 0, which Claude Code treats as "no opinion / allow".
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#
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# Adding a hook is just dropping an executable script into the matching
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# hooks/<event>.d/ directory — no wiring changes required.
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set -euo pipefail
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event="${1:?dispatch.sh needs an event name}"
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here="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
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dir="${here}/$(printf '%s' "$event" | tr '[:upper:]' '[:lower:]').d"
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payload="$(cat)"
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[ -d "$dir" ] || exit 0
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for hook in "$dir"/*.sh; do
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[ -e "$hook" ] || continue
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out="$(printf '%s' "$payload" | bash "$hook" || true)"
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if [ -n "$out" ]; then
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printf '%s\n' "$out"
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exit 0
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fi
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done
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exit 0
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{
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"hooks": {
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"PreToolUse": [
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{
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"matcher": "Bash",
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"hooks": [
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{
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"type": "command",
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"command": "${CLAUDE_PLUGIN_ROOT}/hooks/dispatch.sh PreToolUse"
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}
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]
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}
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]
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}
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}
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Executable
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#!/usr/bin/env bash
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# nix-deploy-output — make `nix run .#deploy` (deploy-rs) logs visible.
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#
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# Symptom this fixes: running `nix run .#deploy` in Claude Code shows an
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# EMPTY command output. deploy-rs and nix draw their progress as an ANSI
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# spinner on a TTY and send activation logs to stderr; when Claude Code
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# captures that, the fancy redraw collapses to nothing and you see a blank.
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#
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# The fix is to force plain, line-buffered output that also captures stderr:
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# piping through `cat` makes nix/deploy-rs detect "not a TTY" and emit plain
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# log lines, and `2>&1` folds stderr (where deploy-rs logs live) into stdout.
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#
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# This hook is a PreToolUse guard on Bash. When it sees a deploy invocation
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# that is NOT already in the output-safe form, it DENIES the call and hands
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# Claude the exact corrected command to run instead. Commands already ending
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# in `2>&1 | cat` (or `2>&1 |cat`) pass through untouched.
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set -euo pipefail
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payload="$(cat)"
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cmd="$(printf '%s' "$payload" | jq -r '.tool_input.command // empty' 2>/dev/null || true)"
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[ -n "$cmd" ] || exit 0
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# Only care about deploy-rs runs: `nix run .#deploy`, `nix run '.#deploy'`,
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# `nix run ".#deploy"`, optionally with a target like `.#deploy.host`.
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printf '%s' "$cmd" | grep -Eq "nix run [\"']?\.#deploy" || exit 0
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# Already output-safe? Must fold stderr into stdout AND defeat TTY detection.
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if printf '%s' "$cmd" | grep -Eq '2>&1' \
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&& printf '%s' "$cmd" | grep -Eq '\|[[:space:]]*(cat|tee|less -R|less)([[:space:]]|$)'; then
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exit 0
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fi
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# Build the corrected command. Strip any trailing pipeline/redirection the
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# model may have already appended, then re-add the canonical suffix.
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base="$(printf '%s' "$cmd" | sed -E 's/[[:space:]]*(2>&1)?[[:space:]]*(\|[[:space:]]*(cat|tee[^|]*|less[^|]*))?[[:space:]]*$//')"
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fixed="${base} 2>&1 | cat"
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reason="deploy-rs / nix draw progress as an ANSI TTY spinner and log to stderr, which Claude Code renders as EMPTY output. Re-run with stderr folded in and output piped through cat to force plain, line-buffered logs:
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${fixed}
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(hooklib:nix-deploy-output)"
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jq -cn --arg r "$reason" '{
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hookSpecificOutput: {
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hookEventName: "PreToolUse",
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permissionDecision: "deny",
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permissionDecisionReason: $r
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}
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}'
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