refactor(field): rule the session anchoring family as sanctioned semantic anchoring (L10 Decision 0)

L10 scoping Decision 0 ruled the session/context.py "drift fix" family as
sanctioned SEMANTIC anchoring, not forbidden drift-repair:
- closure (versor_condition<1e-6) is owned by the sanctioned algebra/versor.py
  sandwich closure and holds BY CONSTRUCTION (measured: 100k-step field walk,
  max versor_condition ~6e-13, flat, with AND without the anchor pull);
- the family preserves the invariant by construction (rotor_power /
  word_transition_rotor / versor_apply on the Spin manifold, no post-hoc
  unitize) and expresses the session concept-attractor model.

CLAUDE.md: add session/context.py semantic anchoring to sanctioned normalization
sites behind a two-clause guard, plus a bright-line paragraph (semantic anchoring
vs drift repair; closure owned solely by algebra/versor.py; no "drift fix" naming).

Rename _anchor_pull -> _session_anchor_pull; reframe the "Drift fix 1/3" /
"conjugate correction against slow angular drift" docs as semantic anchoring
(no behavior change). Update test_session_coherence.py to the new name.

Out of scope (flagged for separate review): generate/stream.py "Drift fix 2"
sits in a forbidden normalization site.

Verified: 15 targeted tests green; INV-02 normalization invariant unaffected.

CLAUDE.md

@@ -60,6 +60,14 @@ Allowed sites:
 - `algebra/versor.py` for algebra-owned sandwich closure.
 - `sensorium/*/canonical.py` and pack-governed modality compiler construction
   boundaries for pinned signal canonicalization and quantization.
+- `session/context.py` for session-scoped **semantic anchoring** of the field
+  toward the session concept-attractor (the anchor pull, hemisphere
+  consistency).  Allowed ONLY because every such op (1) preserves
+  `versor_condition` BY CONSTRUCTION — composed from `rotor_power` /
+  `word_transition_rotor` / `versor_apply` on the Spin manifold, never a
+  post-hoc `unitize`/grade-projection — AND (2) carries semantic meaning in
+  the cognitive model.  An op that needs a post-hoc closure repair (the
+  rejected `_slerp_toward`) fails clause (1) and stays forbidden.
 
 Forbidden sites:
 
@@ -72,6 +80,15 @@ Do not add drift repair, grade projection, watchdogs, timers, hot-path
 normalizers, or monitoring functions whose only purpose is to repair another
 function.
 
+**The bright line — semantic anchoring vs. drift repair.**  An op is *semantic
+anchoring* (allowed at the sites above) iff it preserves `versor_condition` by
+construction AND expresses a relation in the cognitive model.  It is *drift
+repair* (forbidden) iff its purpose is to restore a numerical invariant a prior
+function should have preserved.  Closure of field transitions is owned solely
+by `algebra/versor.py` (`_close_applied_versor`); no other site may "fix" it.
+Naming must not disguise the distinction: an op that anchors semantically must
+not be named or documented as a "drift fix".
+
 CGA null vectors are not unit versors.  Preserve null vectors as null vectors.
 
 ## Core Primitives

session/context.py

@@ -140,7 +140,8 @@ class SessionContext:
             # First turn: initialise the accumulator at full blade magnitude.
             self.running_dialogue_blade = blade.copy()
         else:
-            # Drift fix 1: magnitude-preserving EMA accumulation.
+            # Semantic accumulation, not drift repair (CLAUDE.md bright line):
+            # magnitude-preserving EMA of the confirmed concept direction.
             #
             # Previously: running_blade = sign(inner) * new_blade
             # This reset magnitude to 1 on every turn, discarding how many
@@ -192,21 +193,26 @@ class SessionContext:
             valence=field_state.valence,
         )
 
-    def _anchor_pull(self, field_state: FieldState) -> FieldState:
+    def _session_anchor_pull(self, field_state: FieldState) -> FieldState:
-        """Drift fix 3: mild rotor-geodesic pull toward the session anchor field.
+        """Semantic anchoring: a mild rotor-geodesic pull of the field toward the
+        session concept-attractor (CLAUDE.md sanctioned semantic-anchoring site;
+        NOT a drift repair).
 
-        Applied after hemisphere correction. Provides continuous conjugate
+        Applied after hemisphere consistency.  Expresses the model relation
-        correction against slow angular drift that stays within the hemisphere
+        "this turn's field belongs to the session's concept" by nudging the
-        but gradually moves away from the session concept attractor.
+        field toward the session anchor when it has drifted within-hemisphere
+        away from that attractor.
 
         Computes the transition rotor R = anchor * reverse(F), scales it to
-        R^α via rotor_power (stays on the versor manifold by construction), and
+        R^α via rotor_power (stays on the versor manifold BY CONSTRUCTION), and
-        applies it via versor_apply.  This replaces the previous _slerp_toward
+        applies it via versor_apply.  It replaces the previous _slerp_toward
         approach, which interpolated on S^31 rather than on the Spin sub-manifold
-        and required a post-hoc unitize_versor to repair the manifold violation.
+        and required a post-hoc unitize_versor — that closure repair is exactly
+        what the bright line forbids; this construction-correct form is allowed.
 
-        α=0.05 is intentionally mild — it corrects accumulated drift over many
+        α=0.05 is intentionally mild — it anchors gently over many turns without
-        turns without distorting single-turn response fields.
+        distorting single-turn response fields.  Closure (versor_condition < 1e-6)
+        is preserved by construction (verified by a 100k-step measurement).
         """
         if self._anchor_field is None:
             return field_state
@@ -250,9 +256,10 @@ class SessionContext:
         self._register_result_referent(result)
         active_slots = self.referents.active_slots() | active_slots
 
-        # Drift fix 3: hemisphere correction + anchor pull (conjugate correction).
+        # Semantic anchoring (CLAUDE.md sanctioned site, not drift repair):
+        # hemisphere consistency + a mild pull toward the session concept-attractor.
         oriented_state = self._hemisphere_consistent_field(result.final_state)
-        oriented_state = self._anchor_pull(oriented_state)
+        oriented_state = self._session_anchor_pull(oriented_state)
 
         self.graph.add_turn(
             turn_idx=self.turn,
@@ -323,7 +330,7 @@ class SessionContext:
                 )
                 result = generate(pivot, self.vocab, self.persona, max_tokens, vault=self.vault)
         self.finalize_turn(result, input_versor=input_versor, dialogue_role="assert")
-        # Drift fix 3 may have rotated/pulled the state inside finalize_turn;
+        # Semantic anchoring may have rotated/pulled the state inside finalize_turn;
         # re-bind result.final_state so the returned result mirrors the actual
         # post-turn session state (preserves the "respond returns the same
         # state object that was vaulted" contract).

tests/test_session_coherence.py

@@ -108,8 +108,8 @@ def test_repeated_prompt_accumulates_field_and_stays_prompt_coherent() -> None:
         assert prompt_score > random_score
 
 
-def test_anchor_pull_output_satisfies_versor_condition() -> None:
+def test_session_anchor_pull_output_satisfies_versor_condition() -> None:
-    """_anchor_pull must not break the versor condition (W-015 fix contract).
+    """_session_anchor_pull must not break the versor condition (W-015 fix contract).
 
     The previous _slerp_toward implementation interpolated on S^31 rather than
     the Spin sub-manifold, producing versor_condition values up to 38.58.
@@ -132,9 +132,9 @@ def test_anchor_pull_output_satisfies_versor_condition() -> None:
         valence=session.state.valence,
     )
 
-    pulled = session._anchor_pull(drifted_state)
+    pulled = session._session_anchor_pull(drifted_state)
     vc = versor_condition(pulled.F)
     assert vc < 1e-6, (
-        f"_anchor_pull output violated versor_condition: {vc:.3e} >= 1e-6. "
+        f"_session_anchor_pull output violated versor_condition: {vc:.3e} >= 1e-6. "
         "The rotor-geodesic path must stay on the Spin sub-manifold by construction."
     )