Define independent remote lock objects

docs/internal/artifacts.md

@@ -220,6 +220,21 @@ Caller policy is intentionally outside artifacts helpers:
 - some callers downgrade missing state to status/findings;
 - some callers skip optional behavior when state is missing.
 
+## Remote Lock Objects
+
+The artifacts package defines the independent remote-lock payload and identity
+contract. Each canonical publish source maps to one object below the validated
+session `locks/` prefix; its filename is the lowercase SHA-256 digest of the
+exact source followed by `.lock`.
+
+Lock payloads are strict versioned JSON containing the canonical source, an
+optional reason, and a UTC creation time. Reads are bounded to
+`MaxRemoteLockObjectBytes` (64 KiB), reject unknown fields and trailing values,
+and verify that the payload source matches the key digest. Exact lookup reports
+presence explicitly, prefix listing validates every object and sorts by source,
+creation uses an absence precondition, forced replacement uses one observed
+generation, and removal is idempotent.
+
 ## Key Path Helpers
 
 `internal/artifacts/paths.go` and S3-key helpers define canonical helpers for: