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

tests/test_scribe_marker.py

@@ -36,7 +36,7 @@ INSTANCE = "https://scribe.example.com"
 
 
 def _sh(script: str, cwd: Path, env_extra: dict | None = None) -> str:
-    for tool in ("bash", "jq"):
+    for tool in ("bash",):
         if shutil.which(tool) is None:
             pytest.skip(f"hook runtime tool {tool!r} not installed")
     env = {"PATH": os.environ["PATH"], "HOME": str(cwd)}