t27b ledger: hold a blocked row for self_attention.t27 while its reference is host-dependent #8141

Problem

docs/reports/t27b_expectations.json on master (after #8059, blessed from lab run 6b6386e) has no row for specs/ml/recurrent/self_attention.t27. The spec's reference verdict depends on the host (#8051: its test reads an undefined slice from the undeclared default_input()): the Railway lab's reference fails it, so the bless left it out, while the GitHub runner's reference passes it. t27b-native-ratchet on GitHub therefore reports UNLISTED specs/ml/recurrent/self_attention.t27 (t27b blocked: StmtAssign(undeclared)) on every PR (run 37900879225 on #8059, the same on #7918, #7925, #7905, #8078).

Master's ledger also carries max_not_pass 27 while only 26 rows are non-passing.

Boundary

• Edits only docs/reports/t27b_expectations.json (one row) and adds one docs/now/ entry.
• Does not touch the spec itself: reference: self_attention.t27 passes or fails by host -- its test iterates an undefined W585 scaffold slice (t27b ledger STALE) #8051 (and the queen-8051 salvage) fixes it.
• Data only; no code.

Requirements

• Add {"path": "specs/ml/recurrent/self_attention.t27", "t27b": "blocked", "blocker": "StmtAssign(undeclared)", "reason": "unimplemented"}, sorted, in the shape of the other blocked rows.
• max_not_pass equals the real count of non-passing rows (26 + 1 = 27, so the stored 27 stays).
• The row is held only while the reference is host-dependent; it goes away when reference: self_attention.t27 passes or fails by host -- its test iterates an undefined W585 scaffold slice (t27b ledger STALE) #8051 fixes the spec.

Success Criteria

• Rows sorted, path count equals unique path count, every path exists on the tree.
• t27b-native-ratchet on GitHub reports UNLISTED 0 for self_attention.
• max_not_pass == number of rows whose t27b is neither pass nor pass_vacuous.

Refs #6063 #8051

User Scenarios

• Given the t27b_expectations.json ledger lacks an entry for specs/ml/recurrent/self_attention.t27, When the ledger is updated with a blocked row for that spec, Then t27b-native-ratchet on GitHub reports zero UNLISTED entries for self_attention.t27.
• Given the ledger's max_not_pass value is 27 while only 26 non-passing rows exist, When the blocked row is added bringing the non-passing count to 27, Then max_not_pass equals the actual count of rows whose t27b is neither pass nor pass_vacuous.

Requirements

• FR-001: The ledger docs/reports/t27b_expectations.json MUST contain a row {"path": "specs/ml/recurrent/self_attention.t27", "t27b": "blocked", "blocker": "StmtAssign(undeclared)", "reason": "unimplemented"} sorted among the other blocked rows.
• FR-002: The max_not_pass field in docs/reports/t27b_expectations.json MUST equal the number of rows whose t27b value is neither pass nor pass_vacuous (27 after the addition).
• FR-003: A docs/now/ entry MUST be added documenting this ledger hold for the host-dependent reference.
• FR-004: The rows in docs/reports/t27b_expectations.json MUST remain sorted, have unique paths, and every path MUST exist on the filesystem tree.