feat(ledger): code_shapes — the shape ledger schema (#2787, milestone 294 step 1)

The accounting half of the pattern system (governing note 2786): the snippet
library records canon (small), this table accounts for EVERY extracted shape
(total). Identity is (project, repo_key, path, symbol, kind) — kind included
because one file can define '.foo' (css) and 'foo' (sym) as distinct shapes.
Status vocabulary: canonical / instance / variant / exempt / unclassified,
with unclassified as the default and THE todo state; classifications carry
who judged (agent|audit|hook|mechanical|import), when, and the why for
variants/exemptions. first/last-seen commits + vanished_at keep history
instead of deleting it; a rename reads as vanish+new (accepted for v1).

snippet_id is SET NULL on snippet deletion so accounting rows outlive their
target and rejoin the todo via the step-2 sync, never dangle silently.

Backups: v7 carries code_shapes (judgment data, worth moving) — full and
per-user export sections, and a restore that keeps a judgment only when its
snippet survives the id re-mapping, downgrading to unclassified otherwise.

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

alembic/versions/0079_code_shapes_ledger.py

@@ -0,0 +1,66 @@
+"""The shape ledger: code_shapes (#2787, milestone 294)
+
+Revision ID: 0079
+Revises: 0078
+Create Date: 2026-08-19
+
+The accounting half of the pattern system (governing note 2786): the snippet
+library records canon (small); this table accounts for EVERY shape the
+coverage extractor finds in a bound repo (total). Rows arrive `unclassified`
+from the coverage sync (step 2) and gain judgments — canonical / instance /
+variant / exempt — from audits, hooks, and the mechanical proposer.
+Unclassified IS the todo list.
+"""
+import sqlalchemy as sa
+from alembic import op
+
+revision = "0079"
+down_revision = "0078"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "code_shapes",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "project_id",
+            sa.Integer(),
+            sa.ForeignKey("projects.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("repo_key", sa.Text(), 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("status", sa.Text(), nullable=False, server_default="unclassified"),
+        sa.Column(
+            "snippet_id",
+            sa.BigInteger(),
+            sa.ForeignKey("notes.id", ondelete="SET NULL"),
+            nullable=True,
+        ),
+        sa.Column("reason", sa.Text(), nullable=True),
+        sa.Column("classified_by", sa.Text(), nullable=True),
+        sa.Column("classified_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("first_seen_commit", sa.Text(), nullable=False, server_default=""),
+        sa.Column("last_seen_commit", sa.Text(), nullable=False, server_default=""),
+        sa.Column("vanished_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False),
+        sa.UniqueConstraint(
+            "project_id", "repo_key", "path", "symbol", "kind",
+            name="uq_code_shapes_identity",
+        ),
+    )
+    op.create_index(
+        "ix_code_shapes_project_status", "code_shapes", ["project_id", "status"]
+    )
+    op.create_index("ix_code_shapes_snippet", "code_shapes", ["snippet_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_code_shapes_snippet", table_name="code_shapes")
+    op.drop_index("ix_code_shapes_project_status", table_name="code_shapes")
+    op.drop_table("code_shapes")