refactor(settings): one bounded_float for every numeric bar read from settings

The shape ledger's divergence readout flagged _gate_setting (#4385).
Reading it turned up a family with no canon: floor_for,
get_duplicate_threshold, get_plan_match_threshold and _gate_setting each
parsed a stored string, fell back to the default (never 0) and clamped
into [lo, 1].

- services/settings.bounded_float(raw, default, lo=0, hi=1) is the pure
  parse, fallback and clamp. Each caller keeps its own get_setting read,
  so tests patching get_setting per module still take effect, and
  _gate_setting still fails open on an unreadable setting.
- SettingsView.saveKbInject: eleven inline Math.min/Math.max clamps and
  the local gateAt become one asBar(v, d, lo = 0), mirroring the server.

No behaviour change.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/scribe/services/dedup.py

@@ -287,16 +287,16 @@ def _gate_key(note_type: str) -> str:
 
 
 async def _gate_setting(user_id: int, key: str, lo: float) -> float:
-    from scribe.services.settings import get_setting
+    from scribe.services.settings import bounded_float, get_setting
 
     default = GATE_DEFAULT_THRESHOLDS[key]
     try:
-        value = float(await get_setting(user_id, GATE_THRESHOLD_KEYS[key], str(default)))
+        raw = await get_setting(user_id, GATE_THRESHOLD_KEYS[key], str(default))
     except Exception:
         # Fail-open like the rest of the gate: an unreadable setting falls back
         # to the measured default rather than blocking or waving through.
-        value = default
-    return min(1.0, max(lo, value))
+        raw = None
+    return bounded_float(raw, default, lo)
 
 
 async def gate_bars(user_id: int, note_type: str) -> tuple[float, float]:
@@ -557,16 +557,11 @@ _MAX_DUPLICATE_PAIRS = 200
 
 async def get_duplicate_threshold(user_id: int, kind: str = "snippet") -> float:
     """The user's near-duplicate similarity floor for `kind`, clamped to [0, 1]."""
-    from scribe.services.settings import get_setting
+    from scribe.services.settings import bounded_float, get_setting
 
     default = DUPLICATE_DEFAULT_THRESHOLDS[kind]
-    try:
-        value = float(await get_setting(
-            user_id, DUPLICATE_THRESHOLD_KEYS[kind], str(default)
-        ))
-    except (TypeError, ValueError):
-        value = default
-    return min(1.0, max(0.0, value))
+    raw = await get_setting(user_id, DUPLICATE_THRESHOLD_KEYS[kind], str(default))
+    return bounded_float(raw, default)
 
 
 def group_pairs(pairs: list[tuple[int, int, float]]) -> list[list[int]]:
@@ -1120,15 +1115,12 @@ PLAN_MATCH_DEFAULT_THRESHOLD = 0.80
 
 async def get_plan_match_threshold(user_id: int) -> float:
     """The user's plan-gate similarity floor, clamped to [0, 1]."""
-    from scribe.services.settings import get_setting
+    from scribe.services.settings import bounded_float, get_setting
 
-    try:
-        value = float(await get_setting(
-            user_id, PLAN_MATCH_THRESHOLD_KEY, str(PLAN_MATCH_DEFAULT_THRESHOLD)
-        ))
-    except (TypeError, ValueError):
-        value = PLAN_MATCH_DEFAULT_THRESHOLD
-    return min(1.0, max(0.0, value))
+    raw = await get_setting(
+        user_id, PLAN_MATCH_THRESHOLD_KEY, str(PLAN_MATCH_DEFAULT_THRESHOLD)
+    )
+    return bounded_float(raw, PLAN_MATCH_DEFAULT_THRESHOLD)
 
 
 def plan_candidate_text(

src/scribe/services/retrieval_surfaces.py

@@ -66,7 +66,7 @@ from __future__ import annotations
 
 from dataclasses import dataclass
 
-from scribe.services.settings import get_setting
+from scribe.services.settings import bounded_float, get_setting
 
 # A budget nobody should be able to set past. Not a tuning value — a guard on
 # the worst case, so a mistyped setting cannot turn a menu into a wall of text.
@@ -270,11 +270,8 @@ def dial_for_key(key: str) -> tuple[str, str] | None:
 async def floor_for(user_id: int, name: str) -> float:
     """This install's current floor for a surface, clamped to [0, 1]."""
     s = get_surface(name)
-    try:
-        value = float(await get_setting(user_id, s.floor_key, str(s.floor_default)))
-    except (TypeError, ValueError):
-        value = s.floor_default
-    return min(1.0, max(0.0, value))
+    raw = await get_setting(user_id, s.floor_key, str(s.floor_default))
+    return bounded_float(raw, s.floor_default)
 
 
 async def budget_for(user_id: int, name: str) -> int:

src/scribe/services/settings.py

@@ -16,6 +16,22 @@ logger = logging.getLogger(__name__)
 SECRET_MASK = "********"
 
 
+def bounded_float(raw: str | None, default: float, lo: float = 0.0, hi: float = 1.0) -> float:
+    """A numeric setting as stored text, parsed and clamped to [lo, hi].
+
+    Every similarity bar and retrieval floor is kept as a string and read the
+    same way: an unparseable value falls back to the DEFAULT, never to 0 (a
+    floor of 0 admits everything), and a value out of range is pulled back
+    into it. Pure on purpose: each caller keeps its own `get_setting` read, so
+    what can fail there — and whether that fails open — stays the caller's.
+    """
+    try:
+        value = float(raw)
+    except (TypeError, ValueError):
+        value = default
+    return min(hi, max(lo, value))
+
+
 async def get_admin_setting(key: str, default: str = "") -> str:
     """Read an instance-global setting (one stored on an admin account).