diff --git a/containers/api-proxy/ai-credits-pricing.js b/containers/api-proxy/ai-credits-pricing.js
index 32a962891..589c8dfee 100644
--- a/containers/api-proxy/ai-credits-pricing.js
+++ b/containers/api-proxy/ai-credits-pricing.js
@@ -3,6 +3,12 @@
 // Curated per-model pricing in dollars per 1M tokens.
 // These provider-agnostic aliases take precedence over the bundled models.dev
 // catalog fallback.
+//
+// SYNC NOTE: When adding a new Copilot CLI completion model here, also add it
+// to SUPPORTED_COPILOT_MODELS in src/copilot-model.ts (the host-side validator).
+// If you don't, AWF will reject the COPILOT_MODEL value with a misleading
+// "retired or unsupported" error before any container starts.
+// A CI guard in src/copilot-model-catalog-sync.test.ts enforces this invariant.
 module.exports = Object.freeze({
   'gpt-5-mini':        { input: 0.25,  cachedInput: 0.025, cacheWrite: null, output: 2.00 },
   'gpt-5-codex-mini':  { input: 0.25,  cachedInput: 0.025, cacheWrite: null, output: 2.00 },
diff --git a/src/copilot-model-catalog-sync.test.ts b/src/copilot-model-catalog-sync.test.ts
new file mode 100644
index 000000000..e55e338e5
--- /dev/null
+++ b/src/copilot-model-catalog-sync.test.ts
@@ -0,0 +1,104 @@
+/**
+ * CI guard: verifies that SUPPORTED_COPILOT_MODELS and the api-proxy pricing
+ * catalog stay in sync.
+ *
+ * When a new Copilot CLI completion model is added to
+ * containers/api-proxy/ai-credits-pricing.js, it must ALSO appear in
+ * SUPPORTED_COPILOT_MODELS in src/copilot-model.ts.  Without that, AWF rejects
+ * the COPILOT_MODEL value with a misleading "retired or unsupported" error
+ * before containers even start (as happened with mai-code-1-flash in #5831).
+ *
+ * When adding a new entry to ai-credits-pricing.js, you must either:
+ *   (a) Add the model to SUPPORTED_COPILOT_MODELS in src/copilot-model.ts, OR
+ *   (b) Add it to INTENTIONALLY_EXCLUDED_FROM_SUPPORTED below with a comment
+ *       explaining why it is not a Copilot CLI completion model.
+ */
+
+import * as path from 'path';
+import { testHelpers } from './copilot-model';
+
+/** Mirrors the full canonicalization in copilot-model.ts: lowercase then replace separators. */
+function normalizeSeparators(s: string): string {
+  return s.replace(/[._]/g, '-').toLowerCase();
+}
+
+/**
+ * Models present in ai-credits-pricing.js that are intentionally absent from
+ * SUPPORTED_COPILOT_MODELS.  These are either non-completion models (e.g.
+ * embeddings), BYOK/OpenRouter-only models, or older versioned variants that
+ * the Copilot CLI model picker does not surface.
+ *
+ * Add an entry here (with a comment) only when the model truly should NOT be
+ * settable via COPILOT_MODEL.
+ */
+const INTENTIONALLY_EXCLUDED_FROM_SUPPORTED = new Set([
+  // ── Embedding models — cannot be used as COPILOT_MODEL ────────────────────
+  'text-embedding-3-small', // text embedding, not a chat/completion model
+  'text-embedding-ada-002', // text embedding, not a chat/completion model
+
+  // ── Older Claude Opus 4 versions ──────────────────────────────────────────
+  // Only the latest revision (claude-opus-4.8) is exposed in the Copilot CLI
+  // model picker; older versioned slugs are priced for BYOK/billing purposes.
+  'claude-opus-4-5',
+  'claude-opus-4-6',
+  'claude-opus-4-7',
+
+  // ── Unversioned Claude Sonnet 4 base alias ────────────────────────────────
+  // Use explicit versioned models (claude-sonnet-4.5, claude-sonnet-4.6) instead.
+  'claude-sonnet-4',
+
+  // ── Gemini models not yet available via the Copilot CLI model picker ──────
+  'gemini-2.5-pro',  // older generation
+  'gemini-3-flash',  // not surfaced in Copilot CLI
+  'gemini-3.1-flash', // not surfaced in Copilot CLI (different from gemini-3.1-pro-preview)
+  'gemini-3.1-pro',  // not surfaced in Copilot CLI (different from gemini-3.1-pro-preview)
+
+  // ── GPT variants not in the Copilot CLI model picker ─────────────────────
+  'gpt-5-codex-mini', // internal variant; not a public Copilot CLI model
+  'gpt-5.4-nano',     // not yet surfaced in Copilot CLI
+
+  // ── Internal / experimental models ───────────────────────────────────────
+  'raptor-mini', // internal model; not a public Copilot CLI model
+]);
+
+describe('SUPPORTED_COPILOT_MODELS ↔ ai-credits-pricing catalog sync', () => {
+  const pricingPath = path.resolve(
+    __dirname,
+    '..',
+    'containers',
+    'api-proxy',
+    'ai-credits-pricing.js',
+  );
+
+  // eslint-disable-next-line @typescript-eslint/no-require-imports
+  const pricing = require(pricingPath) as Record<string, unknown>;
+  const pricingModels = Object.keys(pricing);
+
+  it('every Copilot CLI model in ai-credits-pricing.js appears in SUPPORTED_COPILOT_MODELS', () => {
+    // Build a separator-normalised view of the supported set so that
+    // claude-haiku-4-5 (pricing) matches claude-haiku-4.5 (SUPPORTED).
+    const normalizedSupported = new Set(
+      [...testHelpers.supportedCopilotModels].map(m => normalizeSeparators(m)),
+    );
+
+    const missing: string[] = [];
+    for (const model of pricingModels) {
+      if (INTENTIONALLY_EXCLUDED_FROM_SUPPORTED.has(model)) continue;
+      if (!normalizedSupported.has(normalizeSeparators(model))) {
+        missing.push(model);
+      }
+    }
+
+    if (missing.length > 0) {
+      const modelList = missing.map(m => `  '${m}'`).join('\n');
+      throw new Error(
+        `Found ${missing.length} model(s) in containers/api-proxy/ai-credits-pricing.js ` +
+          `that are missing from SUPPORTED_COPILOT_MODELS in src/copilot-model.ts:\n` +
+          `${modelList}\n\n` +
+          `If this is a new Copilot CLI completion model, add it to SUPPORTED_COPILOT_MODELS.\n` +
+          `If it is NOT a Copilot CLI model, add it to INTENTIONALLY_EXCLUDED_FROM_SUPPORTED ` +
+          `in src/copilot-model-catalog-sync.test.ts with a comment explaining why.`,
+      );
+    }
+  });
+});
diff --git a/src/copilot-model.ts b/src/copilot-model.ts
index 0971676e4..fca9578e5 100644
--- a/src/copilot-model.ts
+++ b/src/copilot-model.ts
@@ -25,6 +25,22 @@ const RETIRED_COPILOT_MODEL_ALIASES: Record<string, string> = {
   'gpt-5-codex': 'gpt-5.3-codex',
 };
 
+/**
+ * Single source of truth for all Copilot CLI completion models that AWF accepts
+ * as a `COPILOT_MODEL` value.  The host-side validator rejects any value not in
+ * this set (or its separator-normalised form) before containers start.
+ *
+ * When **adding** a new Copilot CLI model here, also update:
+ *   - `containers/api-proxy/ai-credits-pricing.js`  (AI-credits billing)
+ *   - `docs/model-api-mapping.json`                  (endpoint routing, OpenAI/Anthropic only)
+ *
+ * When **retiring** a model, move it to `RETIRED_COPILOT_MODEL_ALIASES` (below)
+ * and mirror the change in `containers/api-proxy/guards/retired-model-guard.js`.
+ *
+ * A CI guard in `src/copilot-model-catalog-sync.test.ts` fails if any model
+ * present in `ai-credits-pricing.js` is missing from this set (and is not
+ * explicitly listed as a non-CLI model in the test's exclusion set).
+ */
 const SUPPORTED_COPILOT_MODELS = new Set([
   'gpt-4',
   'gpt-4.1',
@@ -91,6 +107,12 @@ function levenshtein(a: string, b: string): number {
   return dp[a.length][b.length];
 }
 
+/** @internal Exposed for unit tests — catalog sync guard uses this to verify pricing parity. */
+// ts-prune-ignore-next
+export const testHelpers = {
+  supportedCopilotModels: new Set(SUPPORTED_COPILOT_MODELS) as ReadonlySet<string>,
+};
+
 export function validateCopilotModel(rawModel: string): CopilotModelValidationResult {
   const trimmed = rawModel.trim();
   if (!trimmed) {