Spec for the gap #4 follow-up from the 1.34.x triage. Builds on
2026-04-15-per-peer-capabilities.md (member-keyed recipient grants)
by adding a sender-side cap subset on session attestations: parent
member signs {session_pubkey, allowed_caps[], expires_at}, broker
enforces intersection of recipient grants × session caps on every
protected operation.
v2 attestation alongside v1 (different canonical prefix
"claudemesh-session-attest-v2|..." → no collision). Default when
no caps subset is declared = full member caps (today's behavior;
opt-in restriction, not breaking).
CLI surface: claudemesh launch --caps dm,read. Bonus: set_state
gate (state-write cap) ships in the same release — closes the
"any session can clobber shared keys like current-pr" footgun.
Migration: dry-run mode for one release before flipping
enforcement. Mirrors the original per-peer-capabilities rollout.
Estimate: ~1 sprint + 1 week dry-run window.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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