diff --git a/src/__tests__/baselines/source-file-lines.json b/src/__tests__/baselines/source-file-lines.json
index 4f04a28da..7cc9a4337 100644
--- a/src/__tests__/baselines/source-file-lines.json
+++ b/src/__tests__/baselines/source-file-lines.json
@@ -1,7 +1,7 @@
 {
   "$comment": "Production files over 800 lines and their length. Maintained by src/__tests__/source-size-ratchet.test.ts.",
   "count": 84,
-  "total": 94692,
+  "total": 94554,
   "entries": {
     "app/medications/page-client.tsx": 839,
     "components/charts/mood-chart.tsx": 1166,
@@ -28,7 +28,7 @@
     "lib/ai/coach/snapshot.ts": 1346,
     "lib/ai/coach/stream-events.ts": 817,
     "lib/ai/coach/types.ts": 1011,
-    "lib/ai/codex-client.ts": 1045,
+    "lib/ai/codex-client.ts": 907,
     "lib/ai/prompts/insight-generator.ts": 1110,
     "lib/ai/provider.ts": 1632,
     "lib/analytics/score/reader.ts": 998,
diff --git a/src/lib/ai/codex-client.ts b/src/lib/ai/codex-client.ts
index 93ad5b38a..2bcef2a08 100644
--- a/src/lib/ai/codex-client.ts
+++ b/src/lib/ai/codex-client.ts
@@ -11,14 +11,14 @@ import type {
   CompletionParams,
   CompletionResult,
 } from "./types";
-import {
-  annotateReasoningDowngrade,
-  isReasoningParameterRejection,
-  learnedReasoningDialect,
-  rememberReasoningDialect,
-} from "./reasoning/dialect-cache";
-import type { ReasoningLevel } from "./reasoning/levels";
 import { levelOfWireEffort, reasoningTitleOf } from "./reasoning/support";
+import {
+  CODEX_ENDPOINT,
+  asksEncryptedReasoning,
+  learnFromReasoningRejection,
+  planCodexReasoning,
+  type CodexReasoningWire,
+} from "./codex-reasoning-wire";
 import {
   getCachedCodexSlug,
   invalidateCachedCodexSlug,
@@ -54,8 +54,6 @@ export { resolveCodexVisionSlug } from "./codex-slug-chain";
  * longer bricks the integration.
  */
 
-const CODEX_ENDPOINT = "https://chatgpt.com/backend-api/codex/responses";
-
 /**
  * Triggers per spec §7b — body / status that mean "this slug is no
  * longer accepted, walk to the next one in the chain".
@@ -207,142 +205,6 @@ function codexStateItems(
   );
 }
 
-// ── v1.41 reasoning wire ────────────────────────────────────────────────────
-
-/**
- * The Responses-API efforts in ascending order. The Codex backend names the
- * values a slug accepts in its 400 body ("Supported values are: 'none',
- * 'low', …"), which is how a slug's ladder is learned.
- */
-const CODEX_EFFORT_ORDER = [
-  "none",
-  "minimal",
-  "low",
-  "medium",
-  "high",
-  "xhigh",
-] as const;
-
-/** What one request sends: `null` is today's `reasoning: null`. */
-type CodexReasoningWire = { effort: string; summary: boolean } | null;
-
-/** What a slug was learned to refuse (see `reasoning/dialect-cache.ts`). */
-interface CodexReasoningDialect {
-  /** The slug refused `reasoning` altogether. */
-  disabled?: true;
-  /** The slug refused `reasoning.summary`. */
-  noSummary?: true;
-  /** The efforts the slug named as supported when it refused one. */
-  efforts?: string[];
-}
-
-function dialectKey(slug: string) {
-  return { provider: "codex", endpoint: CODEX_ENDPOINT, model: slug };
-}
-
-function readCodexDialect(slug: string): CodexReasoningDialect {
-  const raw = learnedReasoningDialect(dialectKey(slug));
-  if (!raw) return {};
-  try {
-    return JSON.parse(raw) as CodexReasoningDialect;
-  } catch {
-    return {};
-  }
-}
-
-function wantedEffort(level: ReasoningLevel): string {
-  // "Off" is a real off on the current slugs: a 2026-10-06 probe answered
-  // `effort: "none"` on gpt-5.5 with a non-reasoning reply. A slug that
-  // refuses it learns its lowest supported value instead.
-  return level === "off" ? "none" : level;
-}
-
-/** The supported effort closest to `wanted` from below, else the lowest. */
-function nearestEffort(wanted: string, supported: string[]): string | null {
-  const rank = (e: string) =>
-    (CODEX_EFFORT_ORDER as readonly string[]).indexOf(e);
-  const known = supported
-    .filter((e) => rank(e) >= 0)
-    .sort((a, b) => rank(a) - rank(b));
-  if (known.length === 0) return null;
-  const below = known.filter((e) => rank(e) <= rank(wanted));
-  return below.length > 0 ? below[below.length - 1] : known[0];
-}
-
-function planCodexReasoning(
-  reasoning: CompletionParams["reasoning"],
-  slug: string,
-): CodexReasoningWire {
-  if (!reasoning) return null;
-  const dialect = readCodexDialect(slug);
-  if (dialect.disabled) return null;
-  let effort: string | null = wantedEffort(reasoning.effort);
-  if (dialect.efforts && !dialect.efforts.includes(effort)) {
-    effort = nearestEffort(effort, dialect.efforts);
-  }
-  if (!effort) return null;
-  return {
-    effort,
-    summary: reasoning.summaries && effort !== "none" && !dialect.noSummary,
-  };
-}
-
-/**
- * True when the request asks for the encrypted reasoning items, the only
- * reasoning state a `store: false` request can hand to the next round.
- */
-function asksEncryptedReasoning(wire: CodexReasoningWire): boolean {
-  return wire !== null && wire.effort !== "none";
-}
-
-/**
- * Read a 400 that refuses a reasoning parameter and learn what the slug
- * accepts instead. Returns the lesser wire to retry with, or `undefined`
- * when the body is not about reasoning (the caller's error path takes it).
- */
-function learnFromReasoningRejection(
-  slug: string,
-  wire: Exclude<CodexReasoningWire, null>,
-  status: number,
-  body: string,
-): CodexReasoningWire | undefined {
-  // Only a 400 that refuses the reasoning parameter counts; a 400 about the
-  // prompt or a tool, and a replay error about a reasoning item handed back
-  // from an earlier round, must not teach the slug anything.
-  if (!isReasoningParameterRejection(status, body, /reasoning/i, slug)) {
-    return undefined;
-  }
-  const dialect = readCodexDialect(slug);
-  let next: CodexReasoningWire;
-  if (wire.summary && /reasoning\.summary|summary/i.test(body)) {
-    dialect.noSummary = true;
-    next = { effort: wire.effort, summary: false };
-  } else {
-    const listed = /supported values are:([^"\n]*)/i.exec(body);
-    const efforts = listed
-      ? Array.from(listed[1].matchAll(/'([a-z]+)'/g), (m) => m[1])
-      : [];
-    const nearest =
-      efforts.length > 0 && !efforts.includes(wire.effort)
-        ? nearestEffort(wire.effort, efforts)
-        : null;
-    if (nearest) {
-      dialect.efforts = efforts;
-      next = { effort: nearest, summary: wire.summary && nearest !== "none" };
-    } else {
-      dialect.disabled = true;
-      next = null;
-    }
-  }
-  rememberReasoningDialect(dialectKey(slug), JSON.stringify(dialect));
-  annotateReasoningDowngrade(
-    "codex",
-    wire.effort,
-    next ? next.effort : "default",
-  );
-  return next;
-}
-
 /**
  * Map tool defs into the Responses `function` tool shape.
  *
diff --git a/src/lib/ai/codex-reasoning-wire.ts b/src/lib/ai/codex-reasoning-wire.ts
new file mode 100644
index 000000000..126740ce0
--- /dev/null
+++ b/src/lib/ai/codex-reasoning-wire.ts
@@ -0,0 +1,152 @@
+/**
+ * The reasoning half of the Codex wire: what `reasoning` field a request
+ * sends for a requested level, and what a slug that refuses it is asked
+ * instead. A slug's refusals are learned per slug in the shared dialect cache
+ * (`reasoning/dialect-cache.ts`), so the next request does not pay the
+ * refused round-trip again.
+ */
+import {
+  annotateReasoningDowngrade,
+  isReasoningParameterRejection,
+  learnedReasoningDialect,
+  rememberReasoningDialect,
+} from "./reasoning/dialect-cache";
+import type { ReasoningLevel } from "./reasoning/levels";
+import type { CompletionParams } from "./types";
+
+/** The responses endpoint, and the key its learned dialects are kept under. */
+export const CODEX_ENDPOINT = "https://chatgpt.com/backend-api/codex/responses";
+
+/**
+ * The Responses-API efforts in ascending order. The Codex backend names the
+ * values a slug accepts in its 400 body ("Supported values are: 'none',
+ * 'low', …"), which is how a slug's ladder is learned.
+ */
+const CODEX_EFFORT_ORDER = [
+  "none",
+  "minimal",
+  "low",
+  "medium",
+  "high",
+  "xhigh",
+] as const;
+
+/** What one request sends: `null` is today's `reasoning: null`. */
+export type CodexReasoningWire = { effort: string; summary: boolean } | null;
+
+/** What a slug was learned to refuse (see `reasoning/dialect-cache.ts`). */
+interface CodexReasoningDialect {
+  /** The slug refused `reasoning` altogether. */
+  disabled?: true;
+  /** The slug refused `reasoning.summary`. */
+  noSummary?: true;
+  /** The efforts the slug named as supported when it refused one. */
+  efforts?: string[];
+}
+
+function dialectKey(slug: string) {
+  return { provider: "codex", endpoint: CODEX_ENDPOINT, model: slug };
+}
+
+function readCodexDialect(slug: string): CodexReasoningDialect {
+  const raw = learnedReasoningDialect(dialectKey(slug));
+  if (!raw) return {};
+  try {
+    return JSON.parse(raw) as CodexReasoningDialect;
+  } catch {
+    return {};
+  }
+}
+
+function wantedEffort(level: ReasoningLevel): string {
+  // "Off" is a real off on the current slugs: a 2026-10-06 probe answered
+  // `effort: "none"` on gpt-5.5 with a non-reasoning reply. A slug that
+  // refuses it learns its lowest supported value instead.
+  return level === "off" ? "none" : level;
+}
+
+/** The supported effort closest to `wanted` from below, else the lowest. */
+function nearestEffort(wanted: string, supported: string[]): string | null {
+  const rank = (e: string) =>
+    (CODEX_EFFORT_ORDER as readonly string[]).indexOf(e);
+  const known = supported
+    .filter((e) => rank(e) >= 0)
+    .sort((a, b) => rank(a) - rank(b));
+  if (known.length === 0) return null;
+  const below = known.filter((e) => rank(e) <= rank(wanted));
+  return below.length > 0 ? below[below.length - 1] : known[0];
+}
+
+export function planCodexReasoning(
+  reasoning: CompletionParams["reasoning"],
+  slug: string,
+): CodexReasoningWire {
+  if (!reasoning) return null;
+  const dialect = readCodexDialect(slug);
+  if (dialect.disabled) return null;
+  let effort: string | null = wantedEffort(reasoning.effort);
+  if (dialect.efforts && !dialect.efforts.includes(effort)) {
+    effort = nearestEffort(effort, dialect.efforts);
+  }
+  if (!effort) return null;
+  return {
+    effort,
+    summary: reasoning.summaries && effort !== "none" && !dialect.noSummary,
+  };
+}
+
+/**
+ * True when the request asks for the encrypted reasoning items, the only
+ * reasoning state a `store: false` request can hand to the next round.
+ */
+export function asksEncryptedReasoning(wire: CodexReasoningWire): boolean {
+  return wire !== null && wire.effort !== "none";
+}
+
+/**
+ * Read a 400 that refuses a reasoning parameter and learn what the slug
+ * accepts instead. Returns the lesser wire to retry with, or `undefined`
+ * when the body is not about reasoning (the caller's error path takes it).
+ */
+export function learnFromReasoningRejection(
+  slug: string,
+  wire: Exclude<CodexReasoningWire, null>,
+  status: number,
+  body: string,
+): CodexReasoningWire | undefined {
+  // Only a 400 that refuses the reasoning parameter counts; a 400 about the
+  // prompt or a tool, and a replay error about a reasoning item handed back
+  // from an earlier round, must not teach the slug anything.
+  if (!isReasoningParameterRejection(status, body, /reasoning/i, slug)) {
+    return undefined;
+  }
+  const dialect = readCodexDialect(slug);
+  let next: CodexReasoningWire;
+  if (wire.summary && /reasoning\.summary|summary/i.test(body)) {
+    dialect.noSummary = true;
+    next = { effort: wire.effort, summary: false };
+  } else {
+    const listed = /supported values are:([^"\n]*)/i.exec(body);
+    const efforts = listed
+      ? Array.from(listed[1].matchAll(/'([a-z]+)'/g), (m) => m[1])
+      : [];
+    const nearest =
+      efforts.length > 0 && !efforts.includes(wire.effort)
+        ? nearestEffort(wire.effort, efforts)
+        : null;
+    if (nearest) {
+      dialect.efforts = efforts;
+      next = { effort: nearest, summary: wire.summary && nearest !== "none" };
+    } else {
+      dialect.disabled = true;
+      next = null;
+    }
+  }
+  rememberReasoningDialect(dialectKey(slug), JSON.stringify(dialect));
+  annotateReasoningDowngrade(
+    "codex",
+    wire.effort,
+    next ? next.effort : "default",
+  );
+  return next;
+}