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_autoinject.sh

@@ -38,14 +38,17 @@ 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
 command -v curl >/dev/null 2>&1 || exit 0
 
 # UserPromptSubmit delivers a JSON event on stdin: { prompt, session_id, cwd, ... }
+# Parsed ONCE into flat lines and then queried three times (#4107): a prompt is
+# the largest payload any hook reads, and re-parsing it per field is three
+# passes over the same text.
 event=$(cat 2>/dev/null || true)
-prompt=$(printf '%s' "$event" | jq -r '.prompt // empty' 2>/dev/null) || prompt=""
-session_id=$(printf '%s' "$event" | jq -r '.session_id // empty' 2>/dev/null) || session_id=""
-event_cwd=$(printf '%s' "$event" | jq -r '.cwd // empty' 2>/dev/null) || event_cwd=""
+event_flat=$(printf '%s' "$event" | scribe_json_flat)
+prompt=$(scribe_json_pick "$event_flat" '.prompt')
+session_id=$(scribe_json_pick "$event_flat" '.session_id')
+event_cwd=$(scribe_json_pick "$event_flat" '.cwd')
 
 # Nothing to retrieve against.
 [ -n "$prompt" ] || exit 0
@@ -59,11 +62,14 @@ scribe_config || exit 0
 # prior-art hook's code cap; this copy was missed when that one was fixed, and
 # scripts/check_plugin.py caught it.
 q=$(printf '%s' "$prompt" | head -c 2000)
-# `-sRr`, not `-rR`: jq -R reads LINE BY LINE, so a multi-line prompt encoded as
-# several lines joined by raw newlines and the request died. Single-line prompts
+# Encoded whole, never line by line. The predecessor here was `jq -rR`, which
+# reads a line at a time: a multi-line prompt came back as several separately
+# encoded lines joined by raw newlines and the request died. Single-line prompts
 # worked, which is why this looked healthy — the long, substantial prompts most
-# worth retrieving against were exactly the ones silently dropped. -s slurps.
-q_enc=$(printf '%s' "$q" | jq -sRr '@uri' 2>/dev/null) || exit 0
+# worth retrieving against were exactly the ones silently dropped. scribe_urlenc
+# reads bytes and has no notion of a line.
+q_enc=$(printf '%s' "$q" | scribe_urlenc) || exit 0
+[ -n "$q_enc" ] || exit 0
 
 # Scope to this directory's project — a `.scribe` marker, else the git remote.
 repo_dir=${event_cwd:-${CLAUDE_PROJECT_DIR:-$PWD}}
@@ -109,22 +115,22 @@ body=$(curl -fsS --max-time 5 \
   "${url%/}/api/plugin/retrieve?q=${q_enc}${repo_q}${exclude_q}" 2>/dev/null) || exit 0
 [ -n "$body" ] || exit 0
 
-context=$(printf '%s' "$body" | jq -r '.context // empty' 2>/dev/null) || exit 0
+body_flat=$(printf '%s' "$body" | scribe_json_flat)
+context=$(scribe_json_pick "$body_flat" '.context')
 [ -n "$context" ] || exit 0
 
 # Remember the surfaced ids so they aren't injected again this session.
 if [ -n "$idfile" ]; then
-  printf '%s' "$body" | jq -r '.note_ids[]? // empty' 2>/dev/null >> "$idfile" || true
+  scribe_json_list "$body_flat" '.note_ids' >> "$idfile" || true
 fi
 # Rules onto the SHARED ledger, stamped so they can age out. Only FRESH ids
 # come back in rule_ids (#3752) — a rule rendered as a repeat is already on
 # the ledger, and re-appending it would keep pushing its stamp forward so it
 # never aged at all.
 if [ -n "$rulefile" ]; then
-  printf '%s' "$body" | jq -r '.rule_ids[]? // empty' 2>/dev/null \
+  scribe_json_list "$body_flat" '.rule_ids' \
     | scribe_rules_append "$rulefile"
 fi
 
-jq -n --arg c "$context" \
-  '{hookSpecificOutput: {hookEventName: "UserPromptSubmit", additionalContext: $c}}'
+scribe_json_out UserPromptSubmit "$context"
 exit 0