diff --git a/openspec/changes/add-format-versioning/.openspec.yaml b/openspec/changes/archive/2026-07-15-add-format-versioning/.openspec.yaml
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rename from openspec/changes/add-format-versioning/.openspec.yaml
rename to openspec/changes/archive/2026-07-15-add-format-versioning/.openspec.yaml
diff --git a/openspec/changes/add-format-versioning/design.md b/openspec/changes/archive/2026-07-15-add-format-versioning/design.md
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rename from openspec/changes/add-format-versioning/design.md
rename to openspec/changes/archive/2026-07-15-add-format-versioning/design.md
diff --git a/openspec/changes/add-format-versioning/proposal.md b/openspec/changes/archive/2026-07-15-add-format-versioning/proposal.md
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rename from openspec/changes/add-format-versioning/proposal.md
rename to openspec/changes/archive/2026-07-15-add-format-versioning/proposal.md
diff --git a/openspec/changes/add-format-versioning/specs/block-graph/spec.md b/openspec/changes/archive/2026-07-15-add-format-versioning/specs/block-graph/spec.md
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rename from openspec/changes/add-format-versioning/specs/block-graph/spec.md
rename to openspec/changes/archive/2026-07-15-add-format-versioning/specs/block-graph/spec.md
diff --git a/openspec/changes/add-format-versioning/tasks.md b/openspec/changes/archive/2026-07-15-add-format-versioning/tasks.md
similarity index 100%
rename from openspec/changes/add-format-versioning/tasks.md
rename to openspec/changes/archive/2026-07-15-add-format-versioning/tasks.md
diff --git a/openspec/specs/block-graph/spec.md b/openspec/specs/block-graph/spec.md
index a2e8bef..4e497eb 100644
--- a/openspec/specs/block-graph/spec.md
+++ b/openspec/specs/block-graph/spec.md
@@ -58,3 +58,53 @@ The in-memory graph and all derived indexes SHALL be updated incrementally on ev
 #### Scenario: Incremental equals rebuild
 - **WHEN** a randomized sequence of at least 1,000 edit operations (create, edit, move, delete, tag, reference) is applied
 - **THEN** the incrementally-maintained indexes are equal to indexes rebuilt from scratch from the Loro document
+
+### Requirement: Graph directory format is versioned
+The graph directory SHALL carry a semantic format version, written at graph
+creation and readable without decoding the Loro document. Opening a graph
+whose format version exceeds the running build's supported version MUST fail
+with an error identifying both versions, without reading or modifying any
+other file in the directory. A graph directory without a version stamp SHALL
+be treated as format version 1 and stamped on next open.
+
+#### Scenario: Newer format is refused untouched
+- **WHEN** a build supporting format 2 opens a graph stamped format 3
+- **THEN** the open fails with an error naming both versions and every file
+  in the graph directory is byte-identical to its pre-open state
+
+#### Scenario: Legacy graph acquires a stamp
+- **WHEN** a graph directory created before versioning existed is opened
+- **THEN** it is treated as format 1, opens normally, and carries a format
+  stamp afterwards
+
+### Requirement: Older formats migrate through a contiguous chain
+Opening a graph with an older format version SHALL migrate it through
+sequential compiled migration steps (each step raising the version by exactly
+one) before normal loading, re-stamping after each step so an interrupted
+migration resumes at the failed step. The registry of migration steps MUST be
+verified contiguous from version 1 to the current version by a test. Before
+the first migration step modifies the directory, the pre-migration snapshot
+MUST be preserved as a backup.
+
+#### Scenario: Migration chain has no gaps
+- **WHEN** the current format version is N
+- **THEN** a test asserts exactly N−1 registered migration steps, so a
+  version bump without its migration fails the build
+
+#### Scenario: Interrupted migration resumes safely
+- **WHEN** the process dies between migration steps
+- **THEN** the next open resumes migration from the recorded intermediate
+  version and completes normally, and the pre-migration snapshot backup
+  still exists
+
+### Requirement: Cross-release open compatibility is continuously verified
+The test suite SHALL include a committed golden graph directory that every
+test run opens and verifies content-identical (block text, structure,
+references) against a recorded expectation. The golden directory SHALL be
+regenerated only together with a deliberate format version bump.
+
+#### Scenario: Dependency upgrade cannot silently break decoding
+- **WHEN** a change (including a Loro version bump) alters how existing graph
+  files are decoded
+- **THEN** the golden-graph test fails, forcing either a fix or an explicit
+  format version bump with a migration