diff --git a/src/resources/extensions/sf/post-execution-checks.js b/src/resources/extensions/sf/post-execution-checks.js
index ee09637f0..9cee22980 100644
--- a/src/resources/extensions/sf/post-execution-checks.js
+++ b/src/resources/extensions/sf/post-execution-checks.js
@@ -14,6 +14,13 @@
  */
 import { existsSync, readFileSync } from "node:fs";
 import { dirname, extname, resolve } from "node:path";
+import { parseRequirementsSections } from "./md-importer.js";
+import { parseRoadmap } from "./parsers.js";
+import {
+	resolveMilestoneFile,
+	resolveSfRootFile,
+	resolveSliceFile,
+} from "./paths.js";
 // ─── Import Resolution Check ─────────────────────────────────────────────────
 /**
  * Extract relative import paths from TypeScript/JavaScript source code.
@@ -363,6 +370,165 @@ function checkNamingConsistency(source, fileName) {
 	}
 	return results;
 }
+// ─── Cross-Slice Consistency Check ───────────────────────────────────────────
+/**
+ * Check whether any key_file in the current task is also referenced by tasks
+ * in other slices. Returns non-blocking warnings for potential conflicts.
+ */
+export function checkCrossSliceConsistency(taskRow, allSliceTasks, _basePath) {
+	const results = [];
+	if (!taskRow.key_files || taskRow.key_files.length === 0) {
+		return [
+			{
+				passed: true,
+				blocking: false,
+				category: "cross-slice",
+				target: taskRow.id,
+				message: "No key files to check for cross-slice consistency",
+			},
+		];
+	}
+	if (!allSliceTasks || allSliceTasks.length === 0) {
+		return [
+			{
+				passed: true,
+				blocking: false,
+				category: "cross-slice",
+				target: taskRow.id,
+				message: "No other slice tasks to check against",
+			},
+		];
+	}
+	const otherSliceTasks = allSliceTasks.filter(
+		(t) =>
+			t.slice_id !== taskRow.slice_id && t.key_files && t.key_files.length > 0,
+	);
+	const conflictingSlices = new Map(); // file → Set(sliceIds)
+	for (const file of taskRow.key_files) {
+		for (const other of otherSliceTasks) {
+			if (other.key_files.includes(file)) {
+				if (!conflictingSlices.has(file)) {
+					conflictingSlices.set(file, new Set());
+				}
+				conflictingSlices.get(file).add(other.slice_id);
+			}
+		}
+	}
+	if (conflictingSlices.size === 0) {
+		return [
+			{
+				passed: true,
+				blocking: false,
+				category: "cross-slice",
+				target: taskRow.id,
+				message: "No cross-slice conflicts detected",
+			},
+		];
+	}
+	for (const [file, sliceIds] of conflictingSlices) {
+		results.push({
+			passed: false,
+			blocking: false,
+			category: "cross-slice",
+			target: file,
+			message: `File '${file}' is also a key file in slice(s) ${Array.from(sliceIds).join(", ")} — verify this is intentional`,
+		});
+	}
+	return results;
+}
+// ─── Milestone Integrity Check ───────────────────────────────────────────────
+/**
+ * Verify milestone-level integrity: completed slices have summaries,
+ * roadmap is consistent, and no active requirements are orphaned.
+ */
+export function checkMilestoneIntegrity(milestoneId, basePath) {
+	const results = [];
+	// Check ROADMAP exists and parse it
+	const roadmapPath = resolveMilestoneFile(basePath, milestoneId, "ROADMAP");
+	if (!roadmapPath || !existsSync(roadmapPath)) {
+		results.push({
+			passed: false,
+			blocking: false,
+			category: "milestone",
+			target: milestoneId,
+			message: `Milestone ROADMAP.md not found for ${milestoneId}`,
+		});
+		return results;
+	}
+	let roadmap;
+	try {
+		const content = readFileSync(roadmapPath, "utf-8");
+		roadmap = parseRoadmap(content);
+	} catch (err) {
+		results.push({
+			passed: false,
+			blocking: false,
+			category: "milestone",
+			target: milestoneId,
+			message: `Failed to parse ROADMAP.md for ${milestoneId}: ${err.message}`,
+		});
+		return results;
+	}
+	// Check that slices marked done in ROADMAP have SUMMARY.md files
+	for (const slice of roadmap.slices) {
+		if (slice.done) {
+			const summaryPath = resolveSliceFile(
+				basePath,
+				milestoneId,
+				slice.id,
+				"SUMMARY",
+			);
+			if (!summaryPath || !existsSync(summaryPath)) {
+				results.push({
+					passed: false,
+					blocking: false,
+					category: "milestone",
+					target: `${milestoneId}/${slice.id}`,
+					message: `Slice ${slice.id} is marked done in ROADMAP but missing SUMMARY.md`,
+				});
+			}
+		}
+	}
+	// Check REQUIREMENTS.md for active requirements belonging to this milestone
+	const reqPath = resolveSfRootFile(basePath, "REQUIREMENTS");
+	if (reqPath && existsSync(reqPath)) {
+		try {
+			const reqContent = readFileSync(reqPath, "utf-8");
+			const requirements = parseRequirementsSections(reqContent);
+			const activeForMilestone = requirements.filter(
+				(r) => r.status === "active" && r.primary_owner === milestoneId,
+			);
+			for (const req of activeForMilestone) {
+				results.push({
+					passed: false,
+					blocking: false,
+					category: "milestone",
+					target: req.id,
+					message: `Active requirement ${req.id} (${req.description || "no description"}) is owned by ${milestoneId} but not yet validated`,
+				});
+			}
+		} catch (err) {
+			results.push({
+				passed: false,
+				blocking: false,
+				category: "milestone",
+				target: milestoneId,
+				message: `Failed to parse REQUIREMENTS.md: ${err.message}`,
+			});
+		}
+	}
+	// If no issues found, return a passing check
+	if (results.length === 0) {
+		results.push({
+			passed: true,
+			blocking: false,
+			category: "milestone",
+			target: milestoneId,
+			message: `Milestone ${milestoneId} integrity checks passed`,
+		});
+	}
+	return results;
+}
 // ─── Main Entry Point ────────────────────────────────────────────────────────
 /**
  * Run all post-execution checks against a completed task.
@@ -370,9 +536,17 @@ function checkNamingConsistency(source, fileName) {
  * @param taskRow - The completed task row
  * @param priorTasks - Array of TaskRow from prior completed tasks in the slice
  * @param basePath - Base path for resolving file references
+ * @param milestoneId - Optional milestone ID for milestone-level checks
+ * @param allSliceTasks - Optional array of all tasks across all slices for cross-slice checks
  * @returns PostExecutionResult with status, checks, and duration
  */
-export function runPostExecutionChecks(taskRow, priorTasks, basePath) {
+export function runPostExecutionChecks(
+	taskRow,
+	priorTasks,
+	basePath,
+	milestoneId,
+	allSliceTasks,
+) {
 	const startTime = Date.now();
 	const allChecks = [];
 	// Run all checks
@@ -384,6 +558,19 @@ export function runPostExecutionChecks(taskRow, priorTasks, basePath) {
 	);
 	const patternChecks = checkPatternConsistency(taskRow, priorTasks, basePath);
 	allChecks.push(...importChecks, ...signatureChecks, ...patternChecks);
+	// New checks: cross-slice consistency and milestone integrity
+	if (allSliceTasks && allSliceTasks.length > 0) {
+		const crossSliceChecks = checkCrossSliceConsistency(
+			taskRow,
+			allSliceTasks,
+			basePath,
+		);
+		allChecks.push(...crossSliceChecks);
+	}
+	if (milestoneId) {
+		const milestoneChecks = checkMilestoneIntegrity(milestoneId, basePath);
+		allChecks.push(...milestoneChecks);
+	}
 	const durationMs = Date.now() - startTime;
 	// Determine overall status
 	const hasBlockingFailure = allChecks.some((c) => !c.passed && c.blocking);
diff --git a/src/resources/extensions/sf/tests/post-execution-checks.test.mjs b/src/resources/extensions/sf/tests/post-execution-checks.test.mjs
new file mode 100644
index 000000000..a88172a87
--- /dev/null
+++ b/src/resources/extensions/sf/tests/post-execution-checks.test.mjs
@@ -0,0 +1,368 @@
+import assert from "node:assert/strict";
+import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { describe, it } from "node:test";
+import {
+	checkCrossSliceConsistency,
+	checkMilestoneIntegrity,
+	runPostExecutionChecks,
+} from "../post-execution-checks.js";
+
+function makeTempDir(prefix) {
+	return mkdtempSync(join(tmpdir(), prefix));
+}
+
+function cleanup(dir) {
+	try {
+		rmSync(dir, { recursive: true, force: true });
+	} catch {}
+}
+
+function writeMilestoneFile(base, milestoneId, fileName, content) {
+	const dir = join(base, ".sf", "milestones", milestoneId);
+	mkdirSync(dir, { recursive: true });
+	writeFileSync(join(dir, fileName), content);
+}
+
+function writeSliceFile(base, milestoneId, sliceId, fileName, content) {
+	const dir = join(base, ".sf", "milestones", milestoneId, "slices", sliceId);
+	mkdirSync(dir, { recursive: true });
+	writeFileSync(join(dir, fileName), content);
+}
+
+// ─── checkCrossSliceConsistency ────────────────────────────────────────────
+
+describe("checkCrossSliceConsistency", () => {
+	it("passes_when_no_other_slice_touches_same_files", () => {
+		const taskRow = {
+			milestone_id: "M001",
+			slice_id: "S03",
+			id: "T01",
+			key_files: ["src/a.ts", "src/b.ts"],
+		};
+		const allSliceTasks = [
+			{
+				milestone_id: "M001",
+				slice_id: "S01",
+				id: "T01",
+				key_files: ["src/c.ts"],
+			},
+			{
+				milestone_id: "M001",
+				slice_id: "S02",
+				id: "T01",
+				key_files: ["src/d.ts"],
+			},
+		];
+		const results = checkCrossSliceConsistency(taskRow, allSliceTasks, "/tmp");
+		assert.equal(results.length, 1);
+		assert.equal(results[0].passed, true);
+		assert.equal(results[0].category, "cross-slice");
+	});
+
+	it("warns_when_another_slice_has_same_key_file", () => {
+		const taskRow = {
+			milestone_id: "M001",
+			slice_id: "S03",
+			id: "T01",
+			key_files: ["src/shared.ts", "src/b.ts"],
+		};
+		const allSliceTasks = [
+			{
+				milestone_id: "M001",
+				slice_id: "S01",
+				id: "T01",
+				key_files: ["src/shared.ts"],
+			},
+			{
+				milestone_id: "M001",
+				slice_id: "S02",
+				id: "T01",
+				key_files: ["src/d.ts"],
+			},
+		];
+		const results = checkCrossSliceConsistency(taskRow, allSliceTasks, "/tmp");
+		assert.equal(results.length, 1);
+		assert.equal(results[0].passed, false);
+		assert.equal(results[0].blocking, false);
+		assert.equal(results[0].category, "cross-slice");
+		assert.ok(results[0].message.includes("src/shared.ts"));
+		assert.ok(results[0].message.includes("S01"));
+	});
+
+	it("ignores_tasks_in_same_slice", () => {
+		const taskRow = {
+			milestone_id: "M001",
+			slice_id: "S03",
+			id: "T02",
+			key_files: ["src/shared.ts"],
+		};
+		const allSliceTasks = [
+			{
+				milestone_id: "M001",
+				slice_id: "S03",
+				id: "T01",
+				key_files: ["src/shared.ts"],
+			},
+		];
+		const results = checkCrossSliceConsistency(taskRow, allSliceTasks, "/tmp");
+		assert.equal(results.length, 1);
+		assert.equal(results[0].passed, true);
+	});
+
+	it("handles_multiple_conflicts", () => {
+		const taskRow = {
+			milestone_id: "M001",
+			slice_id: "S03",
+			id: "T01",
+			key_files: ["src/a.ts", "src/b.ts"],
+		};
+		const allSliceTasks = [
+			{
+				milestone_id: "M001",
+				slice_id: "S01",
+				id: "T01",
+				key_files: ["src/a.ts"],
+			},
+			{
+				milestone_id: "M001",
+				slice_id: "S02",
+				id: "T01",
+				key_files: ["src/b.ts"],
+			},
+		];
+		const results = checkCrossSliceConsistency(taskRow, allSliceTasks, "/tmp");
+		assert.equal(results.length, 2);
+		assert.equal(results[0].passed, false);
+		assert.equal(results[1].passed, false);
+	});
+});
+
+// ─── checkMilestoneIntegrity ───────────────────────────────────────────────
+
+describe("checkMilestoneIntegrity", () => {
+	it("passes_when_all_complete_slices_have_summaries", () => {
+		const base = makeTempDir("sf-pec-mi-");
+		try {
+			writeMilestoneFile(
+				base,
+				"M001",
+				"M001-ROADMAP.md",
+				[
+					"# M001: Test",
+					"",
+					"## Slice Overview",
+					"",
+					"| ID | Slice | Risk | Depends | Done | After this |",
+					"|----|-------|------|---------|------|------------|",
+					"| S01 | S01 | low | — | ✅ | Done. |",
+					"| S02 | S02 | low | — | ⬜ | Pending. |",
+					"",
+				].join("\n"),
+			);
+			writeSliceFile(base, "M001", "S01", "S01-SUMMARY.md", "# S01 Summary\n");
+			writeFileSync(
+				join(base, ".sf", "REQUIREMENTS.md"),
+				[
+					"## Active",
+					"",
+					"### R001 — Test",
+					"- Class: functional",
+					"- Description: test",
+					"- Why: test",
+					"- Source: test",
+					"- Primary owner: M002",
+					"",
+				].join("\n"),
+			);
+
+			const results = checkMilestoneIntegrity("M001", base);
+			assert.ok(
+				results.every((r) => r.passed),
+				`Expected all checks to pass, got: ${JSON.stringify(results)}`,
+			);
+		} finally {
+			cleanup(base);
+		}
+	});
+
+	it("warns_when_complete_slice_lacks_summary", () => {
+		const base = makeTempDir("sf-pec-mi-");
+		try {
+			writeMilestoneFile(
+				base,
+				"M001",
+				"M001-ROADMAP.md",
+				[
+					"# M001: Test",
+					"",
+					"## Slice Overview",
+					"",
+					"| ID | Slice | Risk | Depends | Done | After this |",
+					"|----|-------|------|---------|------|------------|",
+					"| S01 | S01 | low | — | ✅ | Done. |",
+					"",
+				].join("\n"),
+			);
+			// Intentionally NOT writing S01-SUMMARY.md
+			writeFileSync(
+				join(base, ".sf", "REQUIREMENTS.md"),
+				["## Active", "", "### R001 — Test", "- Primary owner: M001", ""].join(
+					"\n",
+				),
+			);
+
+			const results = checkMilestoneIntegrity("M001", base);
+			const missing = results.find((r) => r.message.includes("SUMMARY"));
+			assert.ok(
+				missing,
+				`Expected missing summary warning, got: ${JSON.stringify(results)}`,
+			);
+			assert.equal(missing.passed, false);
+			assert.equal(missing.blocking, false);
+		} finally {
+			cleanup(base);
+		}
+	});
+
+	it("warns_when_active_requirement_belongs_to_milestone", () => {
+		const base = makeTempDir("sf-pec-mi-");
+		try {
+			writeMilestoneFile(
+				base,
+				"M001",
+				"M001-ROADMAP.md",
+				[
+					"# M001: Test",
+					"",
+					"## Slice Overview",
+					"",
+					"| ID | Slice | Risk | Depends | Done | After this |",
+					"|----|-------|------|---------|------|------------|",
+					"| S01 | S01 | low | — | ✅ | Done. |",
+					"",
+				].join("\n"),
+			);
+			writeSliceFile(base, "M001", "S01", "S01-SUMMARY.md", "# S01 Summary\n");
+			writeFileSync(
+				join(base, ".sf", "REQUIREMENTS.md"),
+				[
+					"## Active",
+					"",
+					"### R001 — Test",
+					"- Class: functional",
+					"- Description: test",
+					"- Why: test",
+					"- Source: test",
+					"- Primary owner: M001",
+					"",
+				].join("\n"),
+			);
+
+			const results = checkMilestoneIntegrity("M001", base);
+			const reqWarning = results.find((r) => r.message.includes("R001"));
+			assert.ok(
+				reqWarning,
+				`Expected active requirement warning, got: ${JSON.stringify(results)}`,
+			);
+			assert.equal(reqWarning.passed, false);
+			assert.equal(reqWarning.blocking, false);
+		} finally {
+			cleanup(base);
+		}
+	});
+
+	it("warns_when_roadmap_missing", () => {
+		const base = makeTempDir("sf-pec-mi-");
+		try {
+			mkdirSync(join(base, ".sf"), { recursive: true });
+			writeFileSync(join(base, ".sf", "REQUIREMENTS.md"), "## Active\n\n");
+			const results = checkMilestoneIntegrity("M001", base);
+			const missing = results.find((r) => r.message.includes("ROADMAP"));
+			assert.ok(
+				missing,
+				`Expected missing roadmap warning, got: ${JSON.stringify(results)}`,
+			);
+			assert.equal(missing.passed, false);
+			assert.equal(missing.blocking, false);
+		} finally {
+			cleanup(base);
+		}
+	});
+});
+
+// ─── runPostExecutionChecks ────────────────────────────────────────────────
+
+describe("runPostExecutionChecks", () => {
+	it("includes_cross_slice_and_milestone_checks_when_args_provided", () => {
+		const base = makeTempDir("sf-pec-rpec-");
+		try {
+			writeMilestoneFile(
+				base,
+				"M001",
+				"M001-ROADMAP.md",
+				[
+					"# M001: Test",
+					"",
+					"## Slice Overview",
+					"",
+					"| ID | Slice | Risk | Depends | Done | After this |",
+					"|----|-------|------|---------|------|------------|",
+					"| S01 | S01 | low | — | ✅ | Done. |",
+					"| S02 | S02 | low | — | ⬜ | Pending. |",
+					"",
+				].join("\n"),
+			);
+			writeSliceFile(base, "M001", "S01", "S01-SUMMARY.md", "# S01\n");
+			writeFileSync(join(base, ".sf", "REQUIREMENTS.md"), "## Active\n\n");
+
+			const taskRow = {
+				milestone_id: "M001",
+				slice_id: "S02",
+				id: "T01",
+				key_files: ["src/a.ts"],
+			};
+			const allSliceTasks = [
+				{
+					milestone_id: "M001",
+					slice_id: "S01",
+					id: "T01",
+					key_files: ["src/a.ts"],
+				},
+			];
+
+			const result = runPostExecutionChecks(
+				taskRow,
+				[],
+				base,
+				"M001",
+				allSliceTasks,
+			);
+			const categories = result.checks.map((c) => c.category);
+			assert.ok(
+				categories.includes("cross-slice"),
+				`Expected cross-slice check, got categories: ${categories}`,
+			);
+			assert.ok(
+				categories.includes("milestone"),
+				`Expected milestone check, got categories: ${categories}`,
+			);
+		} finally {
+			cleanup(base);
+		}
+	});
+
+	it("skips_new_checks_when_optional_args_omitted", () => {
+		const taskRow = {
+			milestone_id: "M001",
+			slice_id: "S01",
+			id: "T01",
+			key_files: [],
+		};
+		const result = runPostExecutionChecks(taskRow, [], "/tmp");
+		const categories = result.checks.map((c) => c.category);
+		assert.ok(!categories.includes("cross-slice"));
+		assert.ok(!categories.includes("milestone"));
+	});
+});
diff --git a/src/resources/extensions/sf/uok/auto-verification.js b/src/resources/extensions/sf/uok/auto-verification.js
index fbc282230..3f85c2f30 100644
--- a/src/resources/extensions/sf/uok/auto-verification.js
+++ b/src/resources/extensions/sf/uok/auto-verification.js
@@ -11,6 +11,7 @@
  */
 import { mkdirSync, writeFileSync } from "node:fs";
 import { join } from "node:path";
+import { getErrorMessage } from "../error-utils.js";
 import { loadFile } from "../files.js";
 import { parseRoadmap } from "../parsers.js";
 import { resolveMilestoneFile, resolveSlicePath } from "../paths.js";
@@ -45,7 +46,6 @@ import {
 	formatExecuteTaskRecoveryStatus,
 	inspectExecuteTaskDurability,
 } from "./unit-runtime.js";
-import { getErrorMessage } from "../error-utils.js";
 
 function computeTokenCountFromSession(ctx) {
 	const entries = ctx.sessionManager?.getEntries?.() ?? [];
@@ -568,10 +568,23 @@ export async function runPostUnitVerification(vctx, pauseAuto) {
 								t.sequence < taskRow.sequence,
 						);
 						// Run post-execution checks
+						// Get all tasks across all slices for cross-slice consistency check
+						const allSliceTasks = [];
+						if (mid) {
+							const slices = getMilestoneSlices(mid);
+							for (const slice of slices) {
+								if (slice.id !== sid) {
+									const sliceTasks = getSliceTasks(mid, slice.id);
+									allSliceTasks.push(...sliceTasks);
+								}
+							}
+						}
 						const postExecResult = runPostExecutionChecks(
 							taskRow,
 							priorTasks,
 							s.basePath,
+							mid,
+							allSliceTasks,
 						);
 						// Store checks for evidence JSON
 						postExecChecks = postExecResult.checks;