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_record_opened.sh

@@ -39,23 +39,21 @@
 # here is one extra line, in the direction that shows more rather than less.
 set -uo pipefail
 
+# shellcheck source=plugin/hooks/scribe_defs.sh
+. "$(dirname "${BASH_SOURCE[0]}")/scribe_defs.sh"
+
 event=$(cat 2>/dev/null || true)
 [ -n "$event" ] || exit 0
 
-# No jq, no ledger — and no complaint. Every other hook degrades the same way
-# rather than printing a tooling error in front of the operator's work (#4107
-# tracks making that dependency honest; this is not the place to diverge).
-command -v jq >/dev/null 2>&1 || exit 0
-
-session_id=$(printf '%s' "$event" | jq -r '.session_id // empty' 2>/dev/null) || session_id=""
+event_flat=$(printf '%s' "$event" | scribe_json_flat)
+session_id=$(scribe_json_pick "$event_flat" '.session_id')
 [ -n "$session_id" ] || exit 0
 
 # The matcher in hooks.json already narrows to the get_rule tools, but the
 # server segment of an MCP tool name varies with how the plugin was installed,
 # so the id is read from whichever field is actually present rather than from
 # an assumed tool name. An event that carries none simply records nothing.
-rule_id=$(printf '%s' "$event" \
-  | jq -r '(.tool_input.rule_id // empty) | tostring' 2>/dev/null) || rule_id=""
+rule_id=$(scribe_json_pick "$event_flat" '.tool_input.rule_id')
 rule_id=$(printf '%s' "$rule_id" | tr -cd '0-9')
 [ -n "$rule_id" ] || exit 0
 
@@ -67,9 +65,6 @@ state_dir="${TMPDIR:-/tmp}/scribe-priorart"
 mkdir -p "$state_dir" 2>/dev/null || true
 safe_sid=$(printf '%s' "$session_id" | tr -c 'A-Za-z0-9._-' '_')
 
-# shellcheck source=plugin/hooks/scribe_defs.sh
-. "$(dirname "${BASH_SOURCE[0]}")/scribe_defs.sh"
-
 # Stamped and append-only, exactly like the naming ledger — so the same reader
 # (`scribe_rules_live`) ages both, and the last entry for an id wins.
 printf '%s\n' "$rule_id" | scribe_rules_append "$state_dir/${safe_sid}.opened.ids"