Bind a session to an agent server with safe snapshots and cancellation wiring

[ben-ranford]

Outcome

Synthetic persona: Remote application integrator. Job: Expose an existing session without hand-assembling snapshot metadata or cancellation callbacks.

This is a repository-grounded improvement hypothesis from a synthetic workflow exercise, not validated customer demand.

Evidence

Baseline: 64b0d0d96954 / v1.0.0-rc.2.

• runtime/agent/server.go:48-72,553-614; session/session.go:92-223
• Existing-surface check (executed): go test ./runtime/agent ./replay -count=1 passed
• Feature demand is a synthetic workflow hypothesis supported by the documented surface, not validated customer demand.

Bounded scope

Agent Options requires SnapshotEnvelope and CancelSession while Session already owns Snapshot, Cancel, diagnostics, and lifecycle; add an opt-in bridge that preserves host authorization and action ownership.

Acceptance checks

• A bound session serves full and patch snapshots with valid hashes and revision metadata.
• stave.session.cancel maps to Session.Cancel exactly once.
• Authorization, confirmation, and custom application policy remain explicit inputs.
• Contract tests reject a stale or mismatched envelope.
• Use the documented config/limit ownership map; include redacted diagnostics and deterministic session-close/cancel behavior without replacing app authorization.

Non-goals: No new network transport. No adapter graduation.

Compatibility and dependencies

Additive, opt-in API or separately negotiated extension. Preserve existing root v1 signatures, strict wire decoders, canonical encodings, redaction, limits and application action authority. No root dependency or Go-floor increase is assumed.

Dependencies: #46

Milestone plan and shared release prerequisites: #38. Priority: P1. Required verification must preserve existing gates; completing this issue does not itself authorize a release.