Add verdict state machine

A pure nextVerdict(prev, event, aliases) over lookup results, claims,
named deadlines and errors. Encodes fail closed, monotonic verdicts and
claims that only downgrade, with a transition table and checks over
every event sequence up to length 3.

Adds ADR 0003 and documents the state machine and notifications in
ARCHITECTURE.md.

Author: Aditya292248

ARCHITECTURE.md

@@ -5,24 +5,73 @@
 The verifier watches for an in-progress AgentPhone call to one configured number. For that
 call it asks the platform which agent placed it and which sub-account owns that agent; that
 platform record is the only source of identity ([ADR 0001](docs/adr/0001-trust-anchor.md)).
-It then compares the owner with whoever the caller claims to represent, computes a verdict,
-signs it, and notifies the person being called. Every step that fails, times out or is
-ambiguous ends in `UNVERIFIED` ([ADR 0002](docs/adr/0002-fail-closed.md)).
+As soon as the owner is known, the person being called is told whose agent it is, whether or
+not the agent ever says. If the agent later claims to represent someone else, a second
+message warns them. Every step that fails, times out or is ambiguous ends in `UNVERIFIED`
+([ADR 0002](docs/adr/0002-fail-closed.md)).
 
-Only the skeleton exists so far: config, logging and a health endpoint.
+So far there is config, logging, a health endpoint and the verdict state machine. Nothing
+feeds the state machine real events yet.
 
 ## Code map
 
-| Path            | Role                                                                    |
-| --------------- | ----------------------------------------------------------------------- |
-| `src/config.ts` | Parses and validates the environment. The only reader of `process.env`. |
-| `src/log.ts`    | One-line JSON event log, keyed by call ID.                              |
-| `src/server.ts` | Entry point. `node:http` server; `GET /health` only for now.            |
-| `test/`         | `node:test` suites, run through `tsx`.                                  |
-| `docs/adr/`     | Decision records.                                                       |
+| Path             | Role                                                                    |
+| ---------------- | ----------------------------------------------------------------------- |
+| `src/config.ts`  | Parses and validates the environment. The only reader of `process.env`. |
+| `src/log.ts`     | One-line JSON event log, keyed by call ID.                              |
+| `src/server.ts`  | Entry point. `node:http` server; `GET /health` only for now.            |
+| `src/types.ts`   | Lookup results, claims, verdict states, events and reason codes.        |
+| `src/verdict.ts` | `nextVerdict(prev, event, aliases)`: the pure verdict state machine.    |
+| `test/`          | `node:test` suites, run through `tsx`.                                  |
+| `docs/adr/`      | Decision records.                                                       |
 
-Planned: the AgentPhone client, call lookup, transcript stream, claim extraction, the verdict
-state machine, token signing and the notifier, each in its own module under `src/`.
+Planned: the AgentPhone client, call lookup, transcript stream, claim extraction, token
+signing and the notifier, each in its own module under `src/`.
+
+## Verdict state machine
+
+Every call starts in `IDENTIFYING`. Events are a lookup result, a claim, a deadline (`lookup`
+or `claim`) or an error; `nextVerdict` maps the current state and one event to the next state.
+
+```
+IDENTIFYING ──one match──▶ OWNER_KNOWN ──claim names owner─────────▶ VERIFIED
+     │                          ├──claim names someone else──▶ MISMATCH
+     │                          ├──claim deadline────────────▶ VERIFIED_NO_CLAIM
+     │                          └──error─────────────────────▶ UNVERIFIED
+     └──none / ambiguous / error / lookup deadline──▶ UNVERIFIED
+
+VERIFIED, VERIFIED_NO_CLAIM ──claim names someone else──▶ MISMATCH
+```
+
+- Claims heard in `IDENTIFYING` are kept and checked when the owner is known: one match plus
+  any wrong claim goes straight to `MISMATCH`.
+- In `VERIFIED` and `VERIFIED_NO_CLAIM`, only a claim for someone else changes anything.
+- `MISMATCH` and `UNVERIFIED` are final. Events that do not apply to the current state, such
+  as a late lookup deadline, are ignored.
+
+Its invariants, each checked over every sequence of up to three events in
+`test/verdict.test.ts`:
+
+1. **Fail closed.** No error, timeout, ambiguity or missing call yields `VERIFIED` or
+   `VERIFIED_NO_CLAIM` ([ADR 0002](docs/adr/0002-fail-closed.md)).
+2. **Monotonic.** Once `MISMATCH` or `UNVERIFIED`, the verdict never changes.
+3. **Claims only downgrade.** A claim never creates trust: its only upward move is
+   `OWNER_KNOWN` to `VERIFIED`, and only for the owner's name or alias
+   ([ADR 0003](docs/adr/0003-claim-only-downgrades.md)).
+
+### Notifications
+
+The state machine only computes verdicts; the notifier (not built yet) decides what to send.
+
+| Entering        | Message to the person being called                              |
+| --------------- | --------------------------------------------------------------- |
+| `OWNER_KNOWN`   | Disclosure: whose agent is calling, with a link to the proof    |
+| `MISMATCH`      | Warning: the agent claimed someone other than its owner         |
+| Any other state | Nothing yet; whether `UNVERIFIED` sends a message is still open |
+
+A wrong claim heard before the lookup finishes goes straight from `IDENTIFYING` to
+`MISMATCH`, so the notifier sends the disclosure and the warning together. For the demo, each
+message is a proof-page link printed to the terminal; SMS or iMessage comes later.
 
 ## Invariants
 
@@ -33,6 +82,8 @@ state machine, token signing and the notifier, each in its own module under `src
 - Caller ID and anything the caller says are untrusted input. They can lower a verdict but
   never raise one.
 - The verdict for a call never moves from `MISMATCH` or `UNVERIFIED` back to `VERIFIED`.
+- `src/verdict.ts` does no I/O and reads no clock. Timers live in the caller and arrive as
+  deadline events.
 
 ## Intentional oddities
 

docs/adr/0003-claim-only-downgrades.md

@@ -0,0 +1,42 @@
+# 0003. What the caller claims can only lower the verdict
+
+- Status: Accepted
+- Date: 2026-11-01
+
+## Context
+
+An agent usually says who it is calling for: "I'm Aditya's assistant". That sentence is the
+most natural thing to show the person being called, and also the easiest to fake. Anyone can
+say any name, and a transcript can be wrong. The platform's call record, which links the
+calling agent to the sub-account that owns it, is the only thing the caller cannot choose
+([ADR 0001](0001-trust-anchor.md)).
+
+The person being called is told whose agent it is as soon as the owner is known, so a claim
+is never needed. Still, an agent that says "I'm calling on behalf of Alex" while owned by
+someone else is the most direct form of deception, and the callee may not compare the two
+names themselves. If a claim could raise the verdict, a caller would control part of the
+outcome. If claims are ignored completely, that lie goes unflagged.
+
+## Decision
+
+- Trust comes only from the owner lookup. A claim never creates it.
+- A claim is compared with the owner's name and that owner's aliases, keyed by sub-account
+  ID. The match is exact and case-insensitive, with no partial or fuzzy matching.
+- A claim for anyone else moves the verdict to `MISMATCH`, from `OWNER_KNOWN`, `VERIFIED` or
+  `VERIFIED_NO_CLAIM`. A claim heard before the lookup finishes is kept and checked as soon
+  as the owner is known, so an early claim cannot be lost.
+- A claim that matches the owner can take `OWNER_KNOWN` to `VERIFIED`, and nothing further.
+  It never lifts `VERIFIED_NO_CLAIM`, `MISMATCH` or `UNVERIFIED`.
+- If several claims are heard, one wrong claim outweighs any number of right ones.
+
+## Consequences
+
+- `VERIFIED` and `VERIFIED_NO_CLAIM` are not final: a later claim for someone else still
+  downgrades them. Only `MISMATCH` and `UNVERIFIED` never change.
+- An agent that never names anyone gets `VERIFIED_NO_CLAIM`, not `VERIFIED`. The owner is
+  still disclosed, so the callee knows whose agent it is. The agent never has to do anything
+  for the check: claims are read passively from the call.
+- A real nickname that is not in the alias list shows as `MISMATCH`. A false warning is the
+  accepted cost of never showing a false check mark.
+- Missing a claim (for example, an extraction miss) can only leave the verdict at
+  `VERIFIED_NO_CLAIM`. It can never produce `VERIFIED` for the wrong person.

src/types.ts

@@ -0,0 +1,48 @@
+// Shared shapes for the verdict pipeline. Types only, no logic.
+
+/** Why a call ended UNVERIFIED. */
+export type ReasonCode =
+  | 'lookup_timeout'
+  | 'ambiguous'
+  | 'api_error'
+  | 'no_agentphone_call'
+  | 'transcript_error'
+  // Sent as an error event by the orchestrator when claim extraction itself times out.
+  | 'claim_timeout';
+
+/** The one in-progress AgentPhone call that matched, with the sub-account that owns its agent. */
+export type CallRecord = {
+  kind: 'one';
+  callId: string;
+  agentId: string;
+  ownerSub: string;
+  ownerName: string;
+  from: string;
+  to: string;
+  startedAt: string;
+};
+
+export type LookupResult =
+  | CallRecord
+  | { kind: 'none' }
+  | { kind: 'ambiguous'; count: number }
+  | { kind: 'error'; reason: ReasonCode };
+
+/** What the caller said they represent. Untrusted: it can only lower a verdict. */
+export type ClaimResult = { kind: 'claimed'; principal: string } | { kind: 'none' };
+
+export type Verdict =
+  // Claims heard before the lookup finishes are kept, so an early lie is not lost.
+  | { state: 'IDENTIFYING'; claims: readonly string[] }
+  | { state: 'OWNER_KNOWN'; owner: CallRecord }
+  | { state: 'VERIFIED'; owner: CallRecord; claimed: string }
+  | { state: 'VERIFIED_NO_CLAIM'; owner: CallRecord }
+  | { state: 'MISMATCH'; owner: CallRecord; claimed: string }
+  | { state: 'UNVERIFIED'; reason: ReasonCode };
+
+export type VerdictEvent =
+  | { type: 'lookup'; result: LookupResult }
+  | { type: 'claim'; result: ClaimResult }
+  // Two separate timers: the lookup must finish in time, then the claim window closes.
+  | { type: 'deadline'; which: 'lookup' | 'claim' }
+  | { type: 'error'; reason: ReasonCode };

src/verdict.ts

@@ -0,0 +1,106 @@
+// The verdict state machine. Pure: no I/O, no clock, so every path can be tested.
+import type { CallRecord, LookupResult, ReasonCode, Verdict, VerdictEvent } from './types.js';
+
+/** Extra names per owner, keyed by sub-account ID (the identity anchor), not by name. */
+export type Aliases = ReadonlyMap<string, readonly string[]>;
+
+export const initialVerdict: Verdict = { state: 'IDENTIFYING', claims: [] };
+
+type State<S extends Verdict['state']> = Extract<Verdict, { state: S }>;
+
+export function nextVerdict(prev: Verdict, event: VerdictEvent, aliases: Aliases): Verdict {
+  switch (prev.state) {
+    case 'IDENTIFYING':
+      return fromIdentifying(prev, event, aliases);
+    case 'OWNER_KNOWN':
+      return fromOwnerKnown(prev, event, aliases);
+    case 'VERIFIED':
+    case 'VERIFIED_NO_CLAIM':
+      // A later claim for someone else still downgrades. Nothing else changes an earned verdict.
+      if (event.type === 'claim' && event.result.kind === 'claimed') {
+        const after = withOwner(prev.owner, [event.result.principal], aliases);
+        if (after.state === 'MISMATCH') return after;
+      }
+      return prev;
+    case 'MISMATCH':
+    case 'UNVERIFIED':
+      return prev;
+  }
+}
+
+function fromIdentifying(
+  prev: State<'IDENTIFYING'>,
+  event: VerdictEvent,
+  aliases: Aliases,
+): Verdict {
+  switch (event.type) {
+    case 'lookup':
+      return fromLookup(event.result, prev.claims, aliases);
+    case 'claim':
+      if (event.result.kind === 'none') return prev;
+      return { state: 'IDENTIFYING', claims: [...prev.claims, event.result.principal] };
+    case 'deadline':
+      // The claim window only starts once the owner is known.
+      return event.which === 'lookup' ? unverified('lookup_timeout') : prev;
+    case 'error':
+      return unverified(event.reason);
+  }
+}
+
+function fromLookup(result: LookupResult, claims: readonly string[], aliases: Aliases): Verdict {
+  switch (result.kind) {
+    case 'one':
+      return withOwner(result, claims, aliases);
+    case 'none':
+      return unverified('no_agentphone_call');
+    case 'ambiguous':
+      return unverified('ambiguous');
+    case 'error':
+      return unverified(result.reason);
+  }
+}
+
+function fromOwnerKnown(
+  prev: State<'OWNER_KNOWN'>,
+  event: VerdictEvent,
+  aliases: Aliases,
+): Verdict {
+  switch (event.type) {
+    case 'claim':
+      if (event.result.kind === 'none') return prev;
+      return withOwner(prev.owner, [event.result.principal], aliases);
+    case 'deadline':
+      if (event.which === 'lookup') return prev;
+      return { state: 'VERIFIED_NO_CLAIM', owner: prev.owner };
+    case 'error':
+      return unverified(event.reason);
+    case 'lookup':
+      // Out of order: the owner is already known, and a second lookup cannot replace it.
+      return prev;
+  }
+}
+
+/** Any claim naming someone other than the owner wins: MISMATCH beats VERIFIED. */
+function withOwner(owner: CallRecord, claims: readonly string[], aliases: Aliases): Verdict {
+  const wrong = claims.find((claimed) => !isOwner(owner, claimed, aliases));
+  if (wrong !== undefined) return { state: 'MISMATCH', owner, claimed: wrong };
+  const right = claims[0];
+  if (right !== undefined) return { state: 'VERIFIED', owner, claimed: right };
+  return { state: 'OWNER_KNOWN', owner };
+}
+
+// Exact and case-insensitive. No partial or fuzzy match: a false MISMATCH is safer than a
+// false VERIFIED.
+function isOwner(owner: CallRecord, claimed: string, aliases: Aliases): boolean {
+  const names = [owner.ownerName, ...(aliases.get(owner.ownerSub) ?? [])];
+  const want = normalize(claimed);
+  return names.some((name) => normalize(name) === want);
+}
+
+function normalize(name: string): string {
+  return name.trim().toLowerCase();
+}
+
+function unverified(reason: ReasonCode): Verdict {
+  return { state: 'UNVERIFIED', reason };
+}