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>

alembic/versions/0081_shape_history_and_divergence.py

@@ -0,0 +1,70 @@
+"""Shape history, recheck, and the divergence flag (#2793, milestone 294)
+
+Revision ID: 0081
+Revises: 0080
+Create Date: 2026-08-21
+
+The payoff surface of the ledger. `classified_sha` remembers the fingerprint
+a judgment was made at so a later body change under an instance/variant can
+flag `recheck_at`; `diverges_from` is the button-B flag (a shape new since
+the previous refresh, where one canon dominates its directory+kind, and not
+proposed as that canon). `code_shape_events` is the what-was-used-when
+record: every classification, vanish, reappearance, and drift as it
+happened — history the row alone cannot keep once it moves on.
+"""
+import sqlalchemy as sa
+from alembic import op
+
+revision = "0081"
+down_revision = "0080"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("code_shapes", sa.Column("classified_sha", sa.Text(), nullable=False, server_default=""))
+    op.add_column("code_shapes", sa.Column("recheck_at", sa.DateTime(timezone=True), nullable=True))
+    op.add_column(
+        "code_shapes",
+        sa.Column(
+            "diverges_from",
+            sa.BigInteger(),
+            sa.ForeignKey("notes.id", ondelete="SET NULL"),
+            nullable=True,
+        ),
+    )
+    op.create_index("ix_code_shapes_diverges", "code_shapes", ["project_id", "diverges_from"])
+    op.create_table(
+        "code_shape_events",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "shape_id",
+            sa.Integer(),
+            sa.ForeignKey("code_shapes.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("project_id", sa.Integer(), nullable=False),
+        sa.Column("path", sa.Text(), nullable=False),
+        sa.Column("symbol", sa.Text(), nullable=False),
+        sa.Column("kind", sa.Text(), nullable=False),
+        sa.Column("event", sa.Text(), nullable=False),
+        sa.Column("status", sa.Text(), nullable=True),
+        sa.Column("snippet_id", sa.BigInteger(), nullable=True),
+        sa.Column("classified_by", sa.Text(), nullable=True),
+        sa.Column("reason", sa.Text(), nullable=True),
+        sa.Column("commit", sa.Text(), nullable=False, server_default=""),
+        sa.Column("at", sa.DateTime(timezone=True), nullable=False),
+    )
+    op.create_index("ix_code_shape_events_shape", "code_shape_events", ["shape_id", "at"])
+    op.create_index(
+        "ix_code_shape_events_project_path", "code_shape_events", ["project_id", "path"]
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_code_shape_events_project_path", table_name="code_shape_events")
+    op.drop_index("ix_code_shape_events_shape", table_name="code_shape_events")
+    op.drop_table("code_shape_events")
+    op.drop_index("ix_code_shapes_diverges", table_name="code_shapes")
+    for col in ("diverges_from", "recheck_at", "classified_sha"):
+        op.drop_column("code_shapes", col)