fix(shapes): the semantic arm proposes at the write-path floor, not a private 0.8 (#4208)

0.8 was sized for proposals nobody reads; every semantic proposal is read
by a judge before it is confirmed. Measured, it proposed 0 of 150 while
judged instances of a canon score 0.68-0.71 - the write-path hint's own
floor asks the same question of the same documents at 0.68. The arm now
uses that floor, scans 8 hits instead of 3 (a true instance ranked 4th
behind snippets of other language families), and the proposer version
bumps to 5 so rows examined under the old floor are read again.

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

tests/test_divergence_meaning_gate.py

@@ -11,9 +11,11 @@ do. A signature does not carry a job.
 the floor" and let it withdraw the prompt. Measured live on 2026-09-22 it
 cannot discriminate. Judged instances of the service-unit canon score 0.68–
 0.71 against it at best, most below 0.66; helpers score 0.66–0.75 against
-snippets unrelated to them. Nothing reaches the 0.8 floor, so the "miss"
-fires for nearly every body — the real divergence silenced exactly as the
-helper was. The gate was removed; the prompt asks and the judge answers.
+snippets unrelated to them. The then-floor of 0.8 was reached by nothing, so
+the "miss" fired for nearly every body — the real divergence silenced exactly
+as the helper was. The gate was removed; the prompt asks and the judge
+answers. The same measurement moved the arm's floor down to the write-path
+hint's: 0.8 was sized for proposals nobody reads, and it proposed 0 of 150.
 
 These tests pin what stayed: the arm proposes on a hit and says nothing on a
 miss, the divergence check does not consult it, and the capped pass reads new
@@ -92,6 +94,18 @@ async def test_no_allowed_canon_spends_no_search() -> None:
     mock.assert_not_awaited()
 
 
+async def test_the_arm_proposes_at_the_write_path_floor() -> None:
+    """It asks the write-path hint's question of the same documents, so it
+    uses that surface's floor — not a stricter private one that yields no
+    proposals for the judge to weigh (#4208)."""
+    from scribe.services.plugin_context import WRITEPATH_DEFAULT_THRESHOLD
+
+    mock = _hits()
+    with _patch(mock):
+        await _semantic_canon(1, BODY, {CANON})
+    assert mock.await_args.kwargs["threshold"] == WRITEPATH_DEFAULT_THRESHOLD
+
+
 # ── ...and its silence reaches nothing ───────────────────────────────────