PRISM v2.17.0 — Dispatch round-trip

MINOR, additive (no construct renumbering). Slice 3 of the dependency-ordered
sequence: makes the dispatch round-trip symmetric and named end-to-end, building
on the 2.16 lanes/Desk backbone.

Surface

• Dispatch lifecycle (new §4.15). The whole round-trip named as one bounded
  construct — five stages (build → dispatch → execute → return/converge →
  reconcile), the dispatch-scoped sibling of the engagement lifecycle. A frame
  that subsumes the late-bound build, the operator and return cards, and the
  failure leg by reference (no renumber). Render-from-live-model named once
  across UI view / vendor pick / dispatch paste; Dispatch-builder and
  Dispatch-consumer roles.
• Late-bound build (§6.2). Layer-1 structural completeness now requires a
  pass SPEC, not a frozen Envelope; the Envelope is rendered just-in-time at
  dispatch, anchored to the spec so it cannot silently re-scope.
• Return + failure leg (§4.4). A proactive return-handling card (default
  attach-and-the-session-handles; converge via the seam-③ clean-context
  sub-agent) and a failure leg routed by type — seat-failure (capability null
  → converge + named gap + ranked re-dispatch, never auto), digest/ID mismatch
  (re-grab before converging), substitution (absorb). Substantive divergence is
  the triangulation delta, not a failure.
• Dispatch ID + pinned digest preimage (§3.2 / §4.7). A unique
  per-dispatch-instance identifier paired with the copy-through digest, so a
  re-dispatch of the same pass (identical body ⇒ identical digest) reconciles to
  the exact instance. Reconciliation keys on the triple **filename + Dispatch ID
  • digest**; the digest preimage is pinned for re-stage reproducibility.
• Transport-integrity bracket (§3.2.5). A top-of-paste PRISM PROMPT INTEGRITY anchor + a terminal END PRISM DISPATCHED PASTE sentinel wrap the
  dispatched paste; Self-check Step 0 confirms the sentinel is present and
  its Dispatch ID matches the anchor (presence + string-match, never a hash
  recompute) before any work — so a paste copied mid-stream, before its tail
  finished writing, is caught at the execution session instead of silently
  running partial. The anchor + sentinel are excluded from the digest preimage;
  the bracket frames the triple contract, it is not a fourth block. (Operator
  refinement; adversarially design-verified — the first design keyed on the
  vendor-generated Output block and would have false-halted every paste; the
  terminal-sentinel form is the corrected mechanism.)
• IVD refinement (§4.14 + SP-15). A fanned Independent Validation Dispatch is
  a coverage fan (recall-merge), not triangulation: adjudicate each catch by
  re-derivation, never an agreement vote; prefer strong closed-document
  reasoners as seats. SP-15 gains the "verify contested first-hand" anchor.
• Passive pre-fill of self-report (§4.13). Passively pre-answer
  externally-knowable self-report items before the interview (provenance-tagged),
  triangulated against the self-report when it arrives; passive-only by default,
  active tests need explicit authorization.
• Agentic-browser driver class (§3.6) named as distinct from cowork-mcp
  (investigation-posture single-source); the single-arm paste rule (§4.12).

Calibration / report back

• Does the Dispatch ID close the re-dispatch reconciliation ambiguity in live
  failure-leg runs without adding operator friction?
• Does the late-bound build (spec-not-Envelope) reproduce correctly on long
  engagements, refreshing the rendering without re-scoping?
• Does the proactive return-handling card remove the "what do I do with these
  returns?" ask?

Provenance. Lens Library unchanged (v0.15). Snapshot PRISM_v2_17_0.md
(byte-identical at the v2.17.0 tag). Reference detail in the new Appendix J /
reference/dispatch-conventions.md (promotion map + canonical paste model +
digest-preimage recipe); card schemas in reference/templates.md. Source specs
(Engagements clone): DISPATCH_LIFECYCLE_v1, DISPATCH_CONVENTIONS §A–H,
ML-43/69/73/74. Operator gate confirmed: dispatch-id + pinned preimage.

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Part of the PRISM v2.15.0 → v2.19.0 promotion arc. See RELEASING.md.