diff --git a/src/app/api/insights/chat/__tests__/route-tool-mode.test.ts b/src/app/api/insights/chat/__tests__/route-tool-mode.test.ts
index d8b95d743..3f4a1e17d 100644
--- a/src/app/api/insights/chat/__tests__/route-tool-mode.test.ts
+++ b/src/app/api/insights/chat/__tests__/route-tool-mode.test.ts
@@ -154,6 +154,7 @@ const { buildCoachDataInventory, renderDataInventory, runCoachToolLoop } =
       totalTokens: 80,
       rounds: 2,
       toolTrace: [{ name: "get_metric_series", present: true }],
+      toolResults: [],
     })),
   }));
 vi.mock("@/lib/ai/coach/tools", () => ({
@@ -183,6 +184,9 @@ vi.mock("@/lib/validations/coach-prefs", () => ({
 }));
 
 const { appendMessage } = await import("@/lib/ai/coach/persistence");
+const { parseKeyValuesSentinel } = await import("@/lib/ai/coach/keyvalues");
+const { parseSuggestReminder } =
+  await import("@/lib/ai/coach/suggest-reminder");
 
 vi.mock("@/lib/sse/create-stream", () => ({
   createSseStream: (
@@ -260,6 +264,50 @@ describe("coach chat — tool-mode routing (F1)", () => {
     ).toEqual([{ name: "get_metric_series", present: true }]);
   });
 
+  it("soft-strips a prose number the tools never returned (P6)", async () => {
+    resolveProviderChain.mockResolvedValue([
+      { providerType: "anthropic", instance: {} },
+    ]);
+    // Echo the real prose through the sentinel + suggest parsers so the
+    // verifier sees the model's actual numbers (the default mocks return a
+    // fixed string).
+    const drift = "Your systolic averaged about 138 lately.";
+    (parseKeyValuesSentinel as ReturnType<typeof vi.fn>).mockReturnValue({
+      prose: drift,
+      keyValues: [],
+      malformed: false,
+      malformedEntries: [],
+    });
+    (parseSuggestReminder as ReturnType<typeof vi.fn>).mockReturnValue({
+      prose: drift,
+    });
+    // The tool returned systolic 128; the prose drifts to 138.
+    (runCoachToolLoop as ReturnType<typeof vi.fn>).mockImplementation(
+      async () => ({
+        result: {
+          content: "Your systolic averaged about 138 lately.",
+          tokensUsed: 80,
+          model: "m",
+        },
+        workingProviderType: "anthropic",
+        totalTokens: 80,
+        rounds: 2,
+        toolTrace: [{ name: "get_metric_series", present: true }],
+        toolResults: [
+          { present: true, data: { aggregate: { avgSys30: 128 } } },
+        ],
+      }),
+    );
+    await post(chatReq({ message: "How is my BP?" }));
+    const calls = (appendMessage as ReturnType<typeof vi.fn>).mock.calls;
+    const assistantCall = calls.find(
+      (c) => (c[0] as { role: string }).role === "assistant",
+    );
+    const content = (assistantCall?.[0] as { content: string }).content;
+    expect(content).toContain("[unverified]");
+    expect(content).not.toContain("138");
+  });
+
   it("falls back to the snapshot-stuffing path when a provider lacks tools", async () => {
     resolveProviderChain.mockResolvedValue([
       { providerType: "anthropic", instance: {} },
diff --git a/src/app/api/insights/chat/route.ts b/src/app/api/insights/chat/route.ts
index 341476274..9fca7a8d8 100644
--- a/src/app/api/insights/chat/route.ts
+++ b/src/app/api/insights/chat/route.ts
@@ -84,6 +84,10 @@ import {
 } from "@/lib/ai/coach/tools";
 import type { AiMessage } from "@/lib/ai/types";
 import { parseKeyValuesSentinel } from "@/lib/ai/coach/keyvalues";
+import {
+  findUnverifiedCoachNumbers,
+  stripUnverifiedNumbers,
+} from "@/lib/ai/coach/coach-prose-grounding";
 import { parseSuggestReminder } from "@/lib/ai/coach/suggest-reminder";
 import { gateSuggestion } from "@/lib/ai/coach/suggest-gate";
 import {
@@ -518,6 +522,9 @@ Reply now as the assistant, in ${locale === "de" ? "German" : "English"}.`;
   let result: CompletionResult;
   let workingProviderType: string;
   let toolTrace: CoachToolTrace[] = [];
+  // v1.21.0 (P6) — the present tool-result payloads this turn, for the post-hoc
+  // prose number-verifier. Empty on the no-tools path.
+  let toolResultPayloads: unknown[] = [];
   let totalTokensSpent: number;
   try {
     if (toolMode) {
@@ -556,6 +563,7 @@ Reply now as the assistant, in ${locale === "de" ? "German" : "English"}. Fetch
       result = loop.result;
       workingProviderType = loop.workingProviderType;
       toolTrace = loop.toolTrace;
+      toolResultPayloads = (loop.toolResults ?? []).map((r) => r.data);
       totalTokensSpent = loop.totalTokens;
     } else {
       const fallback = await runRawCompletionWithFallback({
@@ -701,6 +709,38 @@ Reply now as the assistant, in ${locale === "de" ? "German" : "English"}. Fetch
     });
   }
 
+  // v1.21.0 (P6 / C2-5) — post-hoc numeric verifier on the Coach prose. On the
+  // tool path, cross-check every number the model cited against the figures the
+  // tools actually returned this turn; an unmatched number (transcription /
+  // paraphrase drift) is soft-stripped to "[unverified]" and annotated. Cheap,
+  // non-blocking, and a no-op when no tool returned figures (a qualitative turn
+  // or the no-tools path) — the prompt-level grounding rule remains the
+  // backstop there, exactly like the briefing's "no signals → skip". A blocked
+  // turn already carries canned fallback prose, so skip it.
+  if (!outbound.block && toolResultPayloads.length > 0) {
+    const unverified = findUnverifiedCoachNumbers(
+      replyText,
+      toolResultPayloads,
+    );
+    if (unverified.length > 0) {
+      const { prose: corrected, stripped } = stripUnverifiedNumbers(
+        replyText,
+        unverified,
+      );
+      replyText = corrected;
+      annotate({
+        action: { name: "coach.prose.number_unverified" },
+        meta: {
+          flagged: unverified.length,
+          stripped,
+          // No raw values — just the count + truncated tokens for ops triage.
+          tokens: unverified.slice(0, 6).map((u) => u.source),
+          promptVersion: PROMPT_VERSION,
+        },
+      });
+    }
+  }
+
   let surfacedSuggestion: CoachSuggestion | null = null;
   if (!outbound.block && suggestParse.cadence) {
     const decision = await gateSuggestion({
diff --git a/src/lib/ai/coach/__tests__/coach-prose-grounding.test.ts b/src/lib/ai/coach/__tests__/coach-prose-grounding.test.ts
new file mode 100644
index 000000000..c6a61a988
--- /dev/null
+++ b/src/lib/ai/coach/__tests__/coach-prose-grounding.test.ts
@@ -0,0 +1,89 @@
+/**
+ * v1.21.0 (P6 / C2-5) — post-hoc numeric verifier on Coach prose. It must flag
+ * a number the model cited that no tool returned this turn (transcription
+ * drift), exempt structural window/ordinal integers, and no-op when no tool
+ * returned figures. Soft-strip replaces only the flagged tokens.
+ */
+import { describe, expect, it } from "vitest";
+
+import {
+  collectNumericLeaves,
+  findUnverifiedCoachNumbers,
+  stripUnverifiedNumbers,
+} from "@/lib/ai/coach/coach-prose-grounding";
+
+describe("collectNumericLeaves", () => {
+  it("walks numbers, numeric strings, arrays and nested objects", () => {
+    const out = new Set<number>();
+    collectNumericLeaves(
+      {
+        section: { avgSys30: 128, label: "LDL", value: "120" },
+        recent: [{ v: 72 }, { v: "1.2" }],
+      },
+      out,
+    );
+    expect(out.has(128)).toBe(true);
+    expect(out.has(120)).toBe(true);
+    expect(out.has(72)).toBe(true);
+    expect(out.has(1.2)).toBe(true);
+  });
+});
+
+describe("findUnverifiedCoachNumbers", () => {
+  const payloads = [{ aggregate: { avgSys30: 128, avgDia30: 82 } }];
+
+  it("returns nothing when every cited number is grounded", () => {
+    const prose =
+      "Your systolic averaged 128 and diastolic 82 over the last 30 days.";
+    expect(findUnverifiedCoachNumbers(prose, payloads)).toEqual([]);
+  });
+
+  it("flags a drifted number the tools never returned", () => {
+    const prose = "Your systolic averaged about 138 recently.";
+    const findings = findUnverifiedCoachNumbers(prose, payloads);
+    expect(findings).toHaveLength(1);
+    expect(findings[0].value).toBe(138);
+  });
+
+  it("allows a rounding within tolerance", () => {
+    const prose = "Diastolic sat around 82.0 this period.";
+    expect(findUnverifiedCoachNumbers(prose, payloads)).toEqual([]);
+  });
+
+  it("exempts structural window + small-ordinal integers", () => {
+    const prose = "Over the last 30 days, 2 readings stood out of 7 total.";
+    // 30 + 7 are window integers; 2 is a small ordinal — none graded.
+    const findings = findUnverifiedCoachNumbers(prose, [{ x: 999 }]);
+    expect(findings).toEqual([]);
+  });
+
+  it("no-ops when no tool returned any figure", () => {
+    const prose = "Your systolic averaged 138 recently.";
+    expect(findUnverifiedCoachNumbers(prose, [])).toEqual([]);
+    expect(
+      findUnverifiedCoachNumbers(prose, [{ note: "no numbers here" }]),
+    ).toEqual([]);
+  });
+
+  it("returns empty on empty prose", () => {
+    expect(findUnverifiedCoachNumbers("", payloads)).toEqual([]);
+  });
+});
+
+describe("stripUnverifiedNumbers", () => {
+  it("replaces only the flagged tokens, leaving grounded numbers intact", () => {
+    const prose = "Systolic 128, but it spiked to 138 yesterday.";
+    const findings = [{ value: 138, source: "138" }];
+    const { prose: out, stripped } = stripUnverifiedNumbers(prose, findings);
+    expect(stripped).toBe(1);
+    expect(out).toContain("128");
+    expect(out).toContain("[unverified]");
+    expect(out).not.toContain("138");
+  });
+
+  it("is a no-op when nothing was flagged", () => {
+    const { prose, stripped } = stripUnverifiedNumbers("all good", []);
+    expect(prose).toBe("all good");
+    expect(stripped).toBe(0);
+  });
+});
diff --git a/src/lib/ai/coach/__tests__/tools-loop.test.ts b/src/lib/ai/coach/__tests__/tools-loop.test.ts
index 7e70c3499..3c4586224 100644
--- a/src/lib/ai/coach/__tests__/tools-loop.test.ts
+++ b/src/lib/ai/coach/__tests__/tools-loop.test.ts
@@ -86,6 +86,9 @@ describe("runCoachToolLoop", () => {
     expect(out.toolTrace).toEqual([
       { name: "get_metric_series", present: true },
     ]);
+    // v1.21.0 (P6) — the present result's payload is retained for the prose
+    // number-verifier.
+    expect(out.toolResults).toEqual([{ present: true, data: { x: 1 } }]);
     // The second call must forbid tools? No — round 2 still offers them
     // (round <= MAX_ROUNDS). It simply chose to answer.
     expect(runRawCompletionWithFallback).toHaveBeenCalledTimes(2);
diff --git a/src/lib/ai/coach/coach-prose-grounding.ts b/src/lib/ai/coach/coach-prose-grounding.ts
new file mode 100644
index 000000000..0772e83b8
--- /dev/null
+++ b/src/lib/ai/coach/coach-prose-grounding.ts
@@ -0,0 +1,153 @@
+/**
+ * v1.21.0 (P6 / C2-5) — post-hoc numeric verifier for Coach prose.
+ *
+ * The Daily Briefing strips any number absent from the server-computed
+ * `signalsOfDay` block (`@/lib/ai/briefing-grounding`). The Coach's TOOL path
+ * had no equivalent: the addendum forbids citing un-fetched figures, but
+ * nothing deterministically checks the FINAL prose against the figures the
+ * tools actually returned this turn — so a transcription/paraphrase drift
+ * (tool says systolic 128, prose says "~138") could ship.
+ *
+ * This module closes that gap the same way, scoped to the tool path:
+ *   1. Collect every numeric leaf from this turn's PRESENT `CoachToolResult`
+ *      data payloads — the authoritative figure set.
+ *   2. Extract every number the model's prose asserts (reusing the briefing
+ *      verifier's `extractNumbers`).
+ *   3. Flag any prose number that matches no authoritative figure within a
+ *      rounding tolerance, exempting the structural integers (window lengths,
+ *      small ordinals) the briefing verifier already exempts.
+ *
+ * Posture: NON-BLOCKING and cheap. The caller annotates
+ * `coach.prose.number_unverified` and may SOFT-STRIP the unverified figure
+ * from the prose (replacing the bare token with a neutral placeholder) — it
+ * never hard-fails the user's turn. When NO tool returned figures (a
+ * qualitative answer, or the no-tools path) there is no authoritative set to
+ * grade against, so the check no-ops and the prompt-level grounding rule
+ * remains the backstop, exactly like the briefing's "no signals → skip".
+ */
+import { extractNumbers } from "@/lib/ai/briefing-grounding";
+
+/** Absolute + relative tolerance — identical basis to the briefing verifier. */
+const ABS_TOLERANCE = 0.15;
+const REL_TOLERANCE = 0.02;
+
+/**
+ * Window lengths + small ordinals the prose uses structurally ("last 7 days",
+ * "2 of your vitals", "3 readings") — never graded, to avoid false positives on
+ * honest framing. Mirrors the briefing verifier's exemption set.
+ */
+const STRUCTURAL_INTEGERS = new Set([7, 14, 30, 31, 90, 180, 365]);
+
+function isStructural(value: number, raw: string): boolean {
+  if (raw.includes(".") || raw.includes(",")) return false;
+  if (!Number.isInteger(value)) return false;
+  const abs = Math.abs(value);
+  if (abs <= 3) return true;
+  return STRUCTURAL_INTEGERS.has(abs);
+}
+
+/** One prose number that matched no figure any tool returned this turn. */
+export interface UnverifiedCoachNumber {
+  /** The numeric value the model wrote, as parsed. */
+  value: number;
+  /** The raw token the value was read from (truncated). */
+  source: string;
+}
+
+/**
+ * Recursively collect every finite numeric leaf from a tool-result payload —
+ * numbers, and numeric strings ("128", "1.2"). Both forms appear in the
+ * snapshot sections (a mean may be a number; a lab value a string). The set is
+ * deliberately broad so a legitimately-cited figure never trips the verifier;
+ * the verifier's job is only to catch a number the model invented or mis-copied.
+ */
+export function collectNumericLeaves(value: unknown, out: Set<number>): void {
+  if (value === null || value === undefined) return;
+  if (typeof value === "number") {
+    if (Number.isFinite(value)) out.add(value);
+    return;
+  }
+  if (typeof value === "string") {
+    // A scalar numeric string ("128", "-1.2", "92%") — pull its magnitudes.
+    for (const { value: n } of extractNumbers(value)) out.add(n);
+    return;
+  }
+  if (Array.isArray(value)) {
+    for (const item of value) collectNumericLeaves(item, out);
+    return;
+  }
+  if (typeof value === "object") {
+    for (const v of Object.values(value as Record<string, unknown>)) {
+      collectNumericLeaves(v, out);
+    }
+  }
+}
+
+/** True when `value` matches any authoritative figure within tolerance. */
+function isGrounded(
+  value: number,
+  authoritative: ReadonlySet<number>,
+): boolean {
+  for (const a of authoritative) {
+    const tol = Math.max(ABS_TOLERANCE, Math.abs(a) * REL_TOLERANCE);
+    if (Math.abs(value - a) <= tol) return true;
+  }
+  return false;
+}
+
+/**
+ * Find every number the Coach prose asserts that does not trace to a figure
+ * returned by a tool this turn. Returns an empty array when there is no prose,
+ * no authoritative figure set (no present tool result with numbers), or every
+ * cited number is grounded.
+ *
+ * `toolPayloads` is the `data` payload of each PRESENT tool result this turn.
+ */
+export function findUnverifiedCoachNumbers(
+  prose: string,
+  toolPayloads: ReadonlyArray<unknown>,
+): UnverifiedCoachNumber[] {
+  if (!prose) return [];
+  const authoritative = new Set<number>();
+  for (const payload of toolPayloads)
+    collectNumericLeaves(payload, authoritative);
+  // No authoritative figures (a qualitative turn / no-tools path) — nothing to
+  // grade against. The prompt-level grounding rule remains the backstop.
+  if (authoritative.size === 0) return [];
+
+  const findings: UnverifiedCoachNumber[] = [];
+  for (const { value, raw } of extractNumbers(prose)) {
+    if (isStructural(value, raw)) continue;
+    if (isGrounded(value, authoritative)) continue;
+    findings.push({ value, source: raw.slice(0, 32) });
+  }
+  return findings;
+}
+
+/**
+ * Soft-correct the prose: replace each unverified numeric token with a neutral
+ * placeholder so a drifted figure never reaches the user as if authoritative,
+ * while the surrounding qualitative framing is preserved. Conservative — it
+ * only rewrites the exact ungrounded tokens the verifier flagged, and only the
+ * first occurrence of each, leaving every grounded number untouched.
+ *
+ * Returns the (possibly unchanged) prose plus the count of tokens stripped.
+ */
+export function stripUnverifiedNumbers(
+  prose: string,
+  findings: ReadonlyArray<UnverifiedCoachNumber>,
+): { prose: string; stripped: number } {
+  if (findings.length === 0) return { prose, stripped: 0 };
+  let out = prose;
+  let stripped = 0;
+  for (const f of findings) {
+    // Replace the first standalone occurrence of the flagged token. The token
+    // is bounded by non-digit / non-sign edges so we don't clip a larger number.
+    const token = f.source;
+    const idx = out.indexOf(token);
+    if (idx === -1) continue;
+    out = `${out.slice(0, idx)}[unverified]${out.slice(idx + token.length)}`;
+    stripped += 1;
+  }
+  return { prose: out, stripped };
+}
diff --git a/src/lib/ai/coach/tools/loop.ts b/src/lib/ai/coach/tools/loop.ts
index 1f0dfb1d6..5e8208e4a 100644
--- a/src/lib/ai/coach/tools/loop.ts
+++ b/src/lib/ai/coach/tools/loop.ts
@@ -28,7 +28,11 @@ import type { ProviderChainResolved } from "@/lib/ai/provider-runner";
 import type { AiMessage, AiToolDef, CompletionResult } from "@/lib/ai/types";
 import type { ProviderHealthLedger } from "@/lib/ai/provider-health-ledger";
 import type { CoachScopeWindow } from "@/lib/ai/coach/types";
-import { executeCoachTool, type CoachToolTrace } from "./executor";
+import {
+  executeCoachTool,
+  type CoachToolResult,
+  type CoachToolTrace,
+} from "./executor";
 
 export const MAX_ROUNDS = 2;
 /** Absolute ceiling; the final allowed round forces prose (toolChoice none). */
@@ -45,6 +49,13 @@ export interface CoachToolLoopResult {
   rounds: number;
   /** Which tools ran + whether each found data (persisted onto provenance). */
   toolTrace: CoachToolTrace[];
+  /**
+   * v1.21.0 (P6) — the structured payloads of every PRESENT tool result this
+   * turn, in call order. The post-hoc prose number-verifier extracts the
+   * numeric leaves from these to cross-check the figures the model cited. Empty
+   * on a no-tools answer.
+   */
+  toolResults: CoachToolResult[];
 }
 
 export async function runCoachToolLoop(args: {
@@ -78,6 +89,7 @@ export async function runCoachToolLoop(args: {
   let rounds = 0;
   let workingProviderType = "";
   const toolTrace: CoachToolTrace[] = [];
+  const toolResults: CoachToolResult[] = [];
 
   // Round budget: rounds 1..HARD_CAP. On the last allowed round we forbid tool
   // calls so the model must answer.
@@ -120,7 +132,14 @@ export async function runCoachToolLoop(args: {
           forcedFinal: isForcedFinal,
         },
       });
-      return { result, workingProviderType, totalTokens, rounds, toolTrace };
+      return {
+        result,
+        workingProviderType,
+        totalTokens,
+        rounds,
+        toolTrace,
+        toolResults,
+      };
     }
 
     // Append the assistant turn that requested the tools, then execute them in
@@ -140,6 +159,10 @@ export async function runCoachToolLoop(args: {
           fallbackWindow,
         });
         toolTrace.push({ name: call.name, present: toolResult.present });
+        // v1.21.0 (P6) — retain the present results' payloads for the post-hoc
+        // prose number-verifier (the union of numeric leaves grounds the
+        // figures the model may cite).
+        if (toolResult.present) toolResults.push(toolResult);
         return { call, toolResult };
       }),
     );