feat(ledger): divergence readout — button B where button A is canon, shape history, and judged-shape recheck (#2793, milestone 294 step 7)

Every judgment now goes through one helper that remembers the fingerprint
judged (classified_sha) and writes a code_shape_events row; the sync writes
vanished / reappeared / drifted events and flags recheck_at when a body
moves under an instance/variant. The refresh flags diverges_from on shapes
new since the previous computation that sit where one canon dominates the
judged siblings of their directory+kind and were not proposed as that canon
(a first seed flags nothing); the write-path hint asks the same question
in-band for the shapes the hook names. list_shapes(flag=divergence|recheck),
shape_history(project_id, path, symbol) (read-only), coverage line/payload/
card carry divergent + recheck. Backup v8 carries the history. Plugin 0.1.36.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/scribe/models/__init__.py

@@ -44,6 +44,6 @@ from scribe.models.rulebook import (  # noqa: E402, F401
 )
 from scribe.models.repo_binding import RepoBinding  # noqa: E402, F401
 from scribe.models.forge_connection import ForgeConnection  # noqa: E402, F401
-from scribe.models.code_shape import CodeShape  # noqa: E402, F401
+from scribe.models.code_shape import CodeShape, CodeShapeEvent  # noqa: E402, F401
 from scribe.models.system import System, RecordSystem  # noqa: E402, F401
 from scribe.models.design_system import DesignSystem, DesignToken  # noqa: E402, F401

src/scribe/models/code_shape.py

@@ -56,6 +56,15 @@ class CodeShape(Base, TimestampMixin):
     matches on and what a later drift recheck compares against; the ledger
     still never stores code bodies.
 
+    `classified_sha` remembers the fingerprint a judgment was made at;
+    when a later sync sees the body change under an instance/variant, the
+    row is flagged `recheck_at` (the judgment stands, it just asks to be
+    confirmed again) and a `drifted` event is written. `diverges_from`
+    (#2793) is the button-B flag: a shape new since the previous refresh, in
+    a directory+kind where one canon dominates the judged siblings, that the
+    proposer did not match to that canon — "button B appeared where button
+    A is canon: divergence or variant? classify it." Both clear on judgment.
+
     The proposal columns hold the proposer's standing suggestion for an
     UNCLASSIFIED row: `proposed_snippet_id` + `proposal_basis` + score for
     "looks like an instance of #N", or `proposal_basis="derive"` +
@@ -74,6 +83,7 @@ class CodeShape(Base, TimestampMixin):
         Index("ix_code_shapes_project_status", "project_id", "status"),
         Index("ix_code_shapes_snippet", "snippet_id"),
         Index("ix_code_shapes_proposed", "project_id", "proposed_snippet_id"),
+        Index("ix_code_shapes_diverges", "project_id", "diverges_from"),
     )
 
     id: Mapped[int] = mapped_column(primary_key=True)
@@ -110,6 +120,13 @@ class CodeShape(Base, TimestampMixin):
         DateTime(timezone=True), nullable=True
     )
     proposed_sha: Mapped[str] = mapped_column(Text, default="")
+    classified_sha: Mapped[str] = mapped_column(Text, default="")
+    recheck_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
+    diverges_from: Mapped[int | None] = mapped_column(
+        BigInteger, ForeignKey("notes.id", ondelete="SET NULL"), nullable=True
+    )
 
     @property
     def proposal(self) -> dict | None:
@@ -143,6 +160,66 @@ class CodeShape(Base, TimestampMixin):
             "signature": self.signature,
             "body_sha": self.body_sha,
             "proposal": self.proposal,
+            "classified_sha": self.classified_sha,
+            "recheck_at": self.recheck_at.isoformat() if self.recheck_at else None,
+            "diverges_from": self.diverges_from,
             "created_at": self.created_at.isoformat(),
             "updated_at": self.updated_at.isoformat(),
         }
+
+
+# What a shape's history records (#2793). Not "appeared" — first_seen and
+# created_at already say that on the row; history is for what CHANGED:
+SHAPE_EVENTS = ("classified", "vanished", "reappeared", "drifted")
+
+
+class CodeShapeEvent(Base):
+    """One state change in a shape's life — the what-was-used-when record.
+
+    "We used #N here from <date>, #M replaced it at commit C, reason R" is a
+    question the ledger row alone cannot answer once it has moved on; this
+    table keeps each judgment (status, snippet, who, why, at which commit)
+    and each presence change (vanished / reappeared / drifted) as it
+    happened. Denormalised path/symbol/kind so a directory's history reads
+    without joining; `snippet_id` is deliberately FK-free — history outlives
+    the snippet it names, which is the point.
+    """
+
+    __tablename__ = "code_shape_events"
+    __table_args__ = (
+        Index("ix_code_shape_events_shape", "shape_id", "at"),
+        Index("ix_code_shape_events_project_path", "project_id", "path"),
+    )
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    shape_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("code_shapes.id", ondelete="CASCADE"), nullable=False
+    )
+    project_id: Mapped[int] = mapped_column(Integer, nullable=False)
+    path: Mapped[str] = mapped_column(Text, nullable=False)
+    symbol: Mapped[str] = mapped_column(Text, nullable=False)
+    kind: Mapped[str] = mapped_column(Text, nullable=False)
+    event: Mapped[str] = mapped_column(Text, nullable=False)
+    status: Mapped[str | None] = mapped_column(Text, nullable=True)
+    snippet_id: Mapped[int | None] = mapped_column(BigInteger, nullable=True)
+    classified_by: Mapped[str | None] = mapped_column(Text, nullable=True)
+    reason: Mapped[str | None] = mapped_column(Text, nullable=True)
+    commit: Mapped[str] = mapped_column(Text, default="")
+    at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False)
+
+    def to_dict(self) -> dict:
+        return {
+            "id": self.id,
+            "shape_id": self.shape_id,
+            "project_id": self.project_id,
+            "path": self.path,
+            "symbol": self.symbol,
+            "kind": self.kind,
+            "event": self.event,
+            "status": self.status,
+            "snippet_id": self.snippet_id,
+            "classified_by": self.classified_by,
+            "reason": self.reason,
+            "commit": self.commit,
+            "at": self.at.isoformat(),
+        }