fix(plugin): the hooks need no jq and no tac (#4107)

Every hook opened `command -v jq >/dev/null 2>&1 || exit 0`, so on a machine
without jq the operator got no session context, no rules, no prior art and no
process sync — and not one word saying why, because `exit 0` is
indistinguishable from "ran fine, nothing to say". jq is absent by default on
macOS, on the Debian/Ubuntu slim images, on Alpine and in most CI containers.
That is not a prerequisite to document; it is the plugin handing its own
packaging problem to whoever installs it.

`tac` was worse: GNU-only, so the prior-art hook's enclosing-definition arm
did nothing at all on every Mac, silently, from the day it shipped. It is not
replaced but removed — scribe_defs judges each line independently, so
extracting forward and taking `tail -1` is the same answer as reversing and
taking the head, and it drops the early-exit `head` that #4042 was filed for.

No server contract changed, so a lagging plugin cache keeps working.

  scribe_json.awk   JSON -> IDX<TAB>PATH<TAB>VALUE. Two modes: `whole` for an
                    event or a response body, `lines` for a transcript, where
                    an unparseable record is dropped and the rest still read —
                    the `map(try fromjson catch empty)` the jq program opened
                    with. Arrays also report their LENGTH at `[#]`, which is
                    what keeps "zero notes" distinct from "no answer" (#2932).
  scribe_turn.awk   the turn-bounding program, replacing the thirty lines of
                    jq in the Stop hook.
  scribe_defs.sh    scribe_json_flat / _pick / _list / _len / _list_minus read,
                    scribe_json_out writes the envelope (five copies of one
                    shape, gone), scribe_urlenc replaces `jq -sRr '@uri'`.

Percent-encoding goes through `od -tu1` rather than an awk character loop on
purpose: awk's idea of a character follows the locale, so gawk reads an
accented letter as one and mawk as two, and an encoder built on substr() would
emit a different URL depending on which awk is installed. Encoding is defined
on bytes. Verified byte-identical to `jq -sRr '@uri'`.

Measured, not assumed. The per-event path costs 8ms against jq's 3ms. The
transcript path was 70x slower until two fixes: the Stop hook now finds where
the turn starts with a fixed-string grep before parsing (a needle carrying
unescaped quotes cannot occur inside a JSON string, so it matches only at a
record's top level — checked against a full JSON parse of a 27MB transcript:
152 prompt records, 152 matches, no misses, no extras), and the parser reads
each token out of a 1024-byte window instead of copying the rest of the buffer
per token, which was quadratic in line length on the 400KB tool results a
transcript carries.

Differential-tested against the jq program it replaces over 724 windows cut
from three real transcripts — 724 identical, 0 mismatched, 45 of them
exercising a real task close and a real reply. That sweep is what caught
`scribe_turn.awk` never setting FS, which truncated every multi-word reply at
its first space and was invisible to a test whose replies were all empty.

check_plugin.py's `jq -R` lint becomes a guard against either binary coming
back, and three smoke checks lose their `shutil.which("jq")` skip. jq is not
in `ci-python` either, so those three announced a skip on every CI run and had
never once run there: removing the dependency from the product also closed a
permanent hole in its verification. They pass now across all ten hooks.

tests/test_hook_json_reader.py is a differential against Python's `json` over
nested objects, arrays, unicode, escapes, control characters, empty cases and
a value longer than the token window, plus the envelope, the encoder and the
turn analyzer. 139 cases.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

plugin/hooks/scribe_session_context.sh

@@ -49,8 +49,6 @@ set -uo pipefail
 # shellcheck source=plugin/hooks/scribe_defs.sh
 . "$(dirname "${BASH_SOURCE[0]}")/scribe_defs.sh"
 
-command -v jq >/dev/null 2>&1 || exit 0   # needed to emit the JSON envelope safely
-
 # `CDPATH= cd` is deliberate, not a typo'd assignment: it runs this one `cd`
 # with CDPATH empty, so an operator whose CDPATH happens to contain a matching
 # directory name can't send us somewhere else — and `cd` won't echo the resolved
@@ -60,7 +58,8 @@ here=$(CDPATH= cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd) || exit 0
 
 # SessionStart delivers a JSON event on stdin; `source` is startup|resume|compact|clear.
 event=$(cat 2>/dev/null || true)
-source=$(printf '%s' "$event" | jq -r '.source // empty' 2>/dev/null) || source=""
+event_flat=$(printf '%s' "$event" | scribe_json_flat)
+source=$(scribe_json_pick "$event_flat" '.source')
 
 # --- The rule ledger outlives the context it describes (#3749) ---
 #
@@ -127,7 +126,7 @@ source=$(printf '%s' "$event" | jq -r '.source // empty' 2>/dev/null) || source=
 # missed exactly the arm that fires most.
 case "$source" in
   compact|clear)
-    sid=$(printf '%s' "$event" | jq -r '.session_id // empty' 2>/dev/null) || sid=""
+    sid=$(scribe_json_pick "$event_flat" '.session_id')
     if [ -n "$sid" ]; then
       safe_sid=$(printf '%s' "$sid" | tr -c 'A-Za-z0-9._-' '_')
       scribe_clear_session_ledgers "$safe_sid"
@@ -163,7 +162,7 @@ prepend() { if [ -n "$out" ]; then out="$1"$'\n\n---\n\n'"${out}"; else out="$1"
 # appears there.
 manifest="$here/../.claude-plugin/plugin.json"
 if [ -f "$manifest" ]; then
-  plugin_version=$(jq -r '.version // empty' "$manifest" 2>/dev/null) || plugin_version=""
+  plugin_version=$(scribe_json_pick "$(scribe_json_flat < "$manifest")" '.version')
   if [ -n "$plugin_version" ]; then
     append "> Scribe plugin **v${plugin_version}** is executing in this session. A fix merged after this version has not reached it — the marketplace clone updates on its own, but the cache that runs only refreshes when the manifest version changes."
   fi
@@ -193,7 +192,11 @@ if [ -n "$url" ] && [ -n "$token" ] && command -v curl >/dev/null 2>&1; then
   body=$(curl -fsS --max-time 8 \
     -H "Authorization: Bearer ${token}" \
     "${url%/}/api/plugin/context${q}" 2>/dev/null) || body=""
-  [ -n "$body" ] && dyn=$(printf '%s' "$body" | jq -r '.context // empty' 2>/dev/null)
+  body_flat=""
+  if [ -n "$body" ]; then
+    body_flat=$(printf '%s' "$body" | scribe_json_flat)
+    dyn=$(scribe_json_pick "$body_flat" '.context')
+  fi
   # The rules marker is gone with the resident set it described
   # (milestone 394). Nothing is preloaded, so there is no set whose
   # drift a later write could be told about — a rule is retrieved at
@@ -227,7 +230,7 @@ fi
 # server reports whether a project resolved, and this hook — which knows what
 # it sent and why — turns that into the sentence the operator can act on. The
 # repo case is left to the server's existing "bind this repo" hint.
-if [ -n "$dyn" ] && [ -z "$(printf '%s' "$body" | jq -r '.project.id // empty' 2>/dev/null)" ]; then
+if [ -n "$dyn" ] && [ -z "$(scribe_json_pick "$body_flat" '.project.id')" ]; then
   host=$(scribe_url_host "$url")
   if [ -n "$marker_why" ]; then
     append "> ⚠️ Scribe: the marker file \`${marker}\` ${marker_why}, so no project context was loaded. Fix the file, or ignore it and bind this directory another way."
@@ -246,6 +249,5 @@ fi
 # Nothing at all to inject → stay silent.
 [ -n "$out" ] || exit 0
 
-jq -n --arg c "$out" \
-  '{hookSpecificOutput: {hookEventName: "SessionStart", additionalContext: $c}}'
+scribe_json_out SessionStart "$out"
 exit 0