[Yilkash]

Combined PR closing the four assigned spike issues with minimal, verified
primitive slices plus honest spike reports. The full DM-report pipeline,
checkpoint projector, QR/presence UX and UV-gating middleware these issues
ultimately describe do not exist in this codebase today (see per-issue
findings); this PR ships the hard cores each design hangs on, wired only where
a real call site already exists.

Verification

• 23/23 tests pass across 4 new suites (franking-spike,
  checkpoint-finality-spike, session-transfer-spike, session-uv-spike).
• Full npm run typecheck/npm test blocked by a pre-existing broken
  dependency: package.json pins @as-integrations/express (404 on npm)
  while package-lock.json pins the real @as-integrations/express4.
  Untouched per scope rules; verified instead via targeted tsc on the three
  touched TS files (my sections clean; remaining errors pre-existing in
  crypto.ts:46–511 / sessionKey.ts:64 / workerSandbox.ts / types/index.ts)
  and vitest on the 4 new suites.

---

Issue #726: E2E Message Franking

Problem: Report button + moderator view accept unverifiable pasted
plaintext; crypto.ts has E2EE envelopes but zero franking/commitment
constructions; server/lib/alertWebhook.ts is a one-line placeholder and
wsCluster.js carries no per-DM sender/recipient logging.

Resolution: HMAC-commitment franking primitive in src/lib/crypto.ts:
attachFrankingTag/verifyFrankingTag (MAC = truncated HMAC-SHA256 over
nonce‖ciphertext, 16-byte tag, keyId for rotation, constant-time compare,
malformed → false). Report pipeline wiring specced in the spike report
(docs/spikes/726-message-franking-report.md), not faked.

Closes #726

Issue #727: ZK Checkpoint Ledger-Reorg Finality

Problem: Issue describes first-sight-is-final checkpoint handling. Against
current main, server/indexer/parser.ts has no CheckpointCommitted
branch at all and exporter.ts is a contract-state snapshot exporter — the
described pipeline doesn't exist.

Resolution: New server/lib/finality.ts — explicit pending | closed | finalized | orphaned tiers (classifyFinality(depth, {finalityDepth}),
default k=2, throws on garbage depth) + isOrphaned(first, latest)
same-ledger/different-hash predicate. Module is deliberately unwired;
the reorg-aware projection design is specced in
docs/spikes/727-checkpoint-finality-report.md.

Closes #727

Issue #728: Cross-Device Session Transfer

Problem: Issue reports QR session-copy cloning responders across devices.
Current main has no QR flow or presence system: sessionKey.ts is ECDH
with auto-burn, wsCluster.js is a tenant-filtered contract-event relay.

Resolution: Single-use, expiring transfer tickets with generation
semantics in src/lib/sessionKey.ts (createTransferTicket /
redeemTransferTicket, 90s TTL, single-use ticketId, redeem → generation
N+1; replay → already_redeemed, expired → expired). Full presence state
machine + QR UX specced in
docs/spikes/728-session-transfer-report.md.

Closes #728

Issue #729: WebAuthn UV Tiers

Problem: Issue reports uv=preferred downgrading the auth chain. Against
current main the server side is already closed —
server/routes/passkey-auth.js enforces userVerification: 'required' +
requireUserVerification: true on register AND login. What's missing:
sessions carry no UV/capability claim for audit or future step-up gating.

Resolution: uv claim bound into session tokens:
issueSession (uv: opts.uv !== false), preserved through
renewSessionIfNeeded and the three passkey-auth.js call sites
(register/verify, login/verify — measured from the authenticator's answer,
session/refresh). Tier policy + remaining shared-device compartment work
specced in docs/spikes/729-webauthn-uv-tier-report.md.

Closes #729

Covered-slice honesty note

#729 server-side UV enforcement predates this PR (verified in source); this
PR adds the session claim. #727's module is intentionally unwired — there is
no checkpoint pipeline to wire it into. #726/#728 are prototype primitives
without the described DM-report/QR-presence pipelines, which the spike
reports document as remaining work.

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