diff --git a/src/resources/extensions/sf/auto-post-unit.ts b/src/resources/extensions/sf/auto-post-unit.ts
index 63413cd7e..b344312e3 100644
--- a/src/resources/extensions/sf/auto-post-unit.ts
+++ b/src/resources/extensions/sf/auto-post-unit.ts
@@ -1430,6 +1430,24 @@ export async function postUnitPostVerification(
 		}
 	}
 
+	// ── Scaffold-keeper dispatch (ADR-021 Phase D) ──
+	// After milestone completion, fire-and-forget the scaffold-keeper to
+	// detect editing-drift docs and stage `<file>.proposed` artifacts. Failure
+	// is non-fatal and must never break the auto loop, hence the broad try.
+	if (s.currentUnit?.type === "complete-milestone") {
+		try {
+			const { dispatchScaffoldKeeperFireAndForget } = await import(
+				"./scaffold-keeper.js"
+			);
+			dispatchScaffoldKeeperFireAndForget(s.basePath, ctx);
+		} catch (e) {
+			debugLog("postUnit", {
+				phase: "scaffold-keeper-dispatch",
+				error: e instanceof Error ? e.message : String(e),
+			});
+		}
+	}
+
 	// ── Post-unit hooks ──
 	if (s.currentUnit && !s.stepMode) {
 		const hookUnit = checkPostUnitHooks(
diff --git a/src/resources/extensions/sf/auto.ts b/src/resources/extensions/sf/auto.ts
index 2de82eb89..02e520a4d 100644
--- a/src/resources/extensions/sf/auto.ts
+++ b/src/resources/extensions/sf/auto.ts
@@ -946,6 +946,23 @@ export async function stopAuto(
 			});
 		}
 
+		// ── Step 7b: Scaffold-keeper dispatch (ADR-021 Phase D) ──
+		// At session close, detect editing-drift docs and stage `<file>.proposed`
+		// artifacts via the scaffold-keeper. Fire-and-forget — must not block
+		// the cleanup path or break the stop sequence on failure.
+		try {
+			if (ctx && s.basePath) {
+				const { dispatchScaffoldKeeperFireAndForget } = await import(
+					"./scaffold-keeper.js"
+				);
+				dispatchScaffoldKeeperFireAndForget(s.basePath, ctx);
+			}
+		} catch (e) {
+			debugLog("stop-cleanup-scaffold-keeper", {
+				error: e instanceof Error ? e.message : String(e),
+			});
+		}
+
 		// ── Step 8: Ledger notification ──
 		try {
 			// Tag with structured metadata so headless-events.ts classifies via
diff --git a/src/resources/extensions/sf/commands-bootstrap.ts b/src/resources/extensions/sf/commands-bootstrap.ts
index a38f3364c..e7025e2d8 100644
--- a/src/resources/extensions/sf/commands-bootstrap.ts
+++ b/src/resources/extensions/sf/commands-bootstrap.ts
@@ -64,6 +64,10 @@ const TOP_LEVEL_SUBCOMMANDS = [
 		cmd: "codebase",
 		desc: "Generate, refresh, and inspect the codebase map cache",
 	},
+	{
+		cmd: "scaffold",
+		desc: "Inspect or refresh ADR-021 versioned scaffold docs",
+	},
 ] as const;
 
 function filterStartsWith(
@@ -349,6 +353,19 @@ function getSfArgumentCompletions(prefix: string) {
 		);
 	}
 
+	if (parts[0] === "scaffold" && parts.length <= 2) {
+		return filterStartsWith(
+			partial,
+			[
+				{
+					cmd: "sync",
+					desc: "Refresh ADR-021 scaffold docs (drift report + apply pending upgrades)",
+				},
+			],
+			"scaffold",
+		);
+	}
+
 	if (parts[0] === "dispatch" && parts.length <= 2) {
 		return filterStartsWith(
 			partial,
diff --git a/src/resources/extensions/sf/commands-scaffold-sync.ts b/src/resources/extensions/sf/commands-scaffold-sync.ts
new file mode 100644
index 000000000..b92e2af36
--- /dev/null
+++ b/src/resources/extensions/sf/commands-scaffold-sync.ts
@@ -0,0 +1,258 @@
+/**
+ * commands-scaffold-sync.ts — `/sf scaffold sync` (ADR-021 Phase E).
+ *
+ * Manual escape hatch over the Phase C automatic scaffold sync. Lets the user:
+ *  - Inspect drift without modifying anything (`--dry-run`).
+ *  - Force the same operation that would run on next SF startup (default).
+ *  - Run scaffold-keeper synchronously for editing-drift items
+ *    (`--include-editing`) when Phase D has shipped.
+ *  - Restrict the operation to a path glob (`--only=<glob>`).
+ *
+ * The command is intentionally thin: it dispatches to
+ * `ensureAgenticDocsScaffold` and renders `detectScaffoldDrift`. It does not
+ * reimplement either.
+ */
+
+import type { ExtensionCommandContext } from "@singularity-forge/pi-coding-agent";
+
+import { ensureAgenticDocsScaffold } from "./agentic-docs-scaffold.js";
+import { projectRoot } from "./commands/context.js";
+import {
+	detectScaffoldDrift,
+	type ScaffoldDriftItem,
+	type ScaffoldDriftReport,
+} from "./scaffold-drift.js";
+
+export interface ScaffoldSyncOptions {
+	dryRun: boolean;
+	includeEditing: boolean;
+	only?: string;
+}
+
+/** Parse the args string for `/sf scaffold sync`. Tolerates extra whitespace. */
+export function parseScaffoldSyncArgs(args: string): ScaffoldSyncOptions {
+	const trimmed = (args || "").trim();
+	const tokens = trimmed.length > 0 ? trimmed.split(/\s+/) : [];
+	const opts: ScaffoldSyncOptions = {
+		dryRun: false,
+		includeEditing: false,
+	};
+	for (const tok of tokens) {
+		if (tok === "--dry-run") {
+			opts.dryRun = true;
+		} else if (tok === "--include-editing") {
+			opts.includeEditing = true;
+		} else if (tok.startsWith("--only=")) {
+			const value = tok.slice("--only=".length).trim();
+			if (value.length > 0) opts.only = value;
+		}
+	}
+	return opts;
+}
+
+/**
+ * Match a scaffold path against an `--only=<glob>` value.
+ *
+ * Supports the simple cases the brief calls out: `*` is treated as a wildcard,
+ * and as a fallback we accept plain prefix or suffix matches. We deliberately
+ * do not pull in a glob library — Phase E is the escape hatch, not a
+ * production globber.
+ */
+export function matchesOnly(path: string, glob: string | undefined): boolean {
+	if (!glob) return true;
+	if (path === glob) return true;
+	if (glob.includes("*")) {
+		// Build a forgiving regex: escape regex metachars, then turn `*` into `.*`.
+		const pattern = glob
+			.split("*")
+			.map((part) => part.replace(/[.+?^${}()|[\]\\]/g, "\\$&"))
+			.join(".*");
+		try {
+			return new RegExp(`^${pattern}$`).test(path);
+		} catch {
+			return false;
+		}
+	}
+	// Plain string: accept prefix or suffix match. Suffix is useful for
+	// `--only=RELIABILITY.md`; prefix for `--only=harness/`.
+	return path.startsWith(glob) || path.endsWith(glob);
+}
+
+/** Filter a drift report's items by an --only glob. Counts are recomputed. */
+export function applyOnlyFilter(
+	report: ScaffoldDriftReport,
+	only: string | undefined,
+): ScaffoldDriftReport {
+	if (!only) return report;
+	const items = report.items.filter((i) => matchesOnly(i.path, only));
+	const counts: ScaffoldDriftReport["countsByBucket"] = {
+		missing: 0,
+		upgradable: 0,
+		"editing-drift": 0,
+		untracked: 0,
+		customized: 0,
+	};
+	for (const item of items) {
+		counts[item.bucket] += 1;
+	}
+	return {
+		items,
+		countsByBucket: counts,
+		manifestPresent: report.manifestPresent,
+	};
+}
+
+function formatReportTable(report: ScaffoldDriftReport): string {
+	const c = report.countsByBucket;
+	const lines = [
+		"Scaffold drift report:",
+		`  Missing      : ${c.missing}`,
+		`  Upgradable   : ${c.upgradable}`,
+		`  Pending      : ${c.upgradable}`,
+		`  Editing-drift: ${c["editing-drift"]}`,
+		`  Untracked    : ${c.untracked}`,
+		`  Customized   : ${c.customized}`,
+	];
+	const review = report.items.filter(
+		(i) => i.bucket === "missing" || i.bucket === "editing-drift",
+	);
+	if (review.length > 0) {
+		lines.push("");
+		lines.push("Items needing review:");
+		for (const item of review) {
+			lines.push(`  ${item.path}  (${item.bucket})`);
+		}
+	}
+	return lines.join("\n");
+}
+
+/**
+ * Format a brief deltas summary comparing pre- and post-sync drift reports.
+ * Helps the user see at a glance what the sync actually did.
+ */
+function formatSyncDelta(
+	before: ScaffoldDriftReport,
+	after: ScaffoldDriftReport,
+): string | null {
+	const wroteMissing = before.countsByBucket.missing - after.countsByBucket.missing;
+	const upgraded = before.countsByBucket.upgradable - after.countsByBucket.upgradable;
+	const promoted = before.countsByBucket.untracked - after.countsByBucket.untracked;
+	if (wroteMissing <= 0 && upgraded <= 0 && promoted <= 0) return null;
+	const parts: string[] = [];
+	if (wroteMissing > 0) parts.push(`wrote ${wroteMissing} missing`);
+	if (upgraded > 0) parts.push(`refreshed ${upgraded} pending`);
+	if (promoted > 0) parts.push(`promoted ${promoted} legacy-matched`);
+	return `Sync complete — ${parts.join(", ")}.`;
+}
+
+/**
+ * Lazy import for Phase D's scaffold-keeper dispatcher. Returns `null` if
+ * Phase D has not shipped yet, in which case `--include-editing` reports the
+ * feature as unavailable rather than crashing.
+ */
+async function tryLoadScaffoldKeeper(): Promise<
+	| ((basePath: string, items: ScaffoldDriftItem[]) => Promise<{ proposed: string[] }>)
+	| null
+> {
+	try {
+		// Phase D is expected to expose this from a `scaffold-keeper.js` sibling.
+		const mod: unknown = await import("./scaffold-keeper.js").catch(() => null);
+		if (
+			mod &&
+			typeof (mod as { dispatchScaffoldKeeperIfNeeded?: unknown })
+				.dispatchScaffoldKeeperIfNeeded === "function"
+		) {
+			return (
+				mod as {
+					dispatchScaffoldKeeperIfNeeded: (
+						basePath: string,
+						items: ScaffoldDriftItem[],
+					) => Promise<{ proposed: string[] }>;
+				}
+			).dispatchScaffoldKeeperIfNeeded;
+		}
+	} catch {
+		// fall through
+	}
+	return null;
+}
+
+/**
+ * Top-level handler for `/sf scaffold sync [args]`.
+ *
+ * Always notifies via `ctx.ui.notify` — never throws on the sync paths
+ * themselves; underlying calls (`ensureAgenticDocsScaffold`,
+ * `detectScaffoldDrift`) are non-throwing per their contracts.
+ */
+export async function handleScaffoldSync(
+	args: string,
+	ctx: ExtensionCommandContext,
+): Promise<void> {
+	const opts = parseScaffoldSyncArgs(args);
+	const basePath = projectRoot();
+
+	// Dry-run: report only, no filesystem mutation.
+	if (opts.dryRun) {
+		const report = applyOnlyFilter(detectScaffoldDrift(basePath), opts.only);
+		ctx.ui.notify(formatReportTable(report), "info");
+		return;
+	}
+
+	// Default: run the same automatic-mode entry point, then report.
+	const before = applyOnlyFilter(detectScaffoldDrift(basePath), opts.only);
+	try {
+		ensureAgenticDocsScaffold(basePath);
+	} catch (err) {
+		ctx.ui.notify(
+			`Scaffold sync failed: ${(err as Error).message}`,
+			"warning",
+		);
+		return;
+	}
+	const after = applyOnlyFilter(detectScaffoldDrift(basePath), opts.only);
+
+	const delta = formatSyncDelta(before, after);
+	const reportText = formatReportTable(after);
+	const message = delta ? `${delta}\n\n${reportText}` : reportText;
+	ctx.ui.notify(message, "info");
+
+	if (!opts.includeEditing) return;
+
+	// --include-editing: synchronously dispatch Phase D's keeper for editing-drift.
+	const editingItems = after.items.filter((i) => i.bucket === "editing-drift");
+	if (editingItems.length === 0) {
+		ctx.ui.notify("No editing-drift items to merge.", "info");
+		return;
+	}
+
+	const dispatcher = await tryLoadScaffoldKeeper();
+	if (!dispatcher) {
+		ctx.ui.notify(
+			"--include-editing: scaffold-keeper not yet available (ADR-021 Phase D pending).",
+			"warning",
+		);
+		return;
+	}
+
+	try {
+		const result = await dispatcher(basePath, editingItems);
+		const proposed = Array.isArray(result?.proposed) ? result.proposed : [];
+		if (proposed.length === 0) {
+			ctx.ui.notify(
+				"scaffold-keeper completed without producing .proposed files.",
+				"info",
+			);
+			return;
+		}
+		const lines = [
+			`Wrote ${proposed.length} .proposed file${proposed.length === 1 ? "" : "s"}:`,
+			...proposed.map((p) => `  ${p}`),
+		];
+		ctx.ui.notify(lines.join("\n"), "info");
+	} catch (err) {
+		ctx.ui.notify(
+			`scaffold-keeper failed: ${(err as Error).message}`,
+			"warning",
+		);
+	}
+}
diff --git a/src/resources/extensions/sf/commands/catalog.ts b/src/resources/extensions/sf/commands/catalog.ts
index eea2ae379..df94ba2d1 100644
--- a/src/resources/extensions/sf/commands/catalog.ts
+++ b/src/resources/extensions/sf/commands/catalog.ts
@@ -18,7 +18,7 @@ export interface SfCommandDefinition {
 type CompletionMap = Record<string, readonly SfCommandDefinition[]>;
 
 export const SF_COMMAND_DESCRIPTION =
-	"SF — Singularity Forge: /sf help|start|templates|next|autonomous|auto|stop|pause|status|widget|visualize|queue|quick|discuss|capture|triage|todo|dispatch|history|undo|undo-task|reset-slice|rate|skip|export|cleanup|model|mode|prefs|config|keys|hooks|run-hook|skill-health|doctor|logs|forensics|changelog|migrate|remote|steer|knowledge|harness|new-milestone|parallel|cmux|park|unpark|init|setup|inspect|extensions|update|fast|mcp|rethink|codebase|notifications|ship|do|session-report|backlog|pr-branch|add-tests|scan";
+	"SF — Singularity Forge: /sf help|start|templates|next|autonomous|auto|stop|pause|status|widget|visualize|queue|quick|discuss|capture|triage|todo|dispatch|history|undo|undo-task|reset-slice|rate|skip|export|cleanup|model|mode|prefs|config|keys|hooks|run-hook|skill-health|doctor|logs|forensics|changelog|migrate|remote|steer|knowledge|harness|new-milestone|parallel|cmux|park|unpark|init|setup|inspect|extensions|update|fast|mcp|rethink|codebase|notifications|ship|do|session-report|backlog|pr-branch|add-tests|scan|scaffold";
 
 export const TOP_LEVEL_SUBCOMMANDS: readonly SfCommandDefinition[] = [
 	{ cmd: "help", desc: "Categorized command reference with descriptions" },
@@ -155,6 +155,10 @@ export const TOP_LEVEL_SUBCOMMANDS: readonly SfCommandDefinition[] = [
 	{ cmd: "backlog", desc: "Manage backlog items (add, promote, remove, list)" },
 	{ cmd: "pr-branch", desc: "Create clean PR branch filtering .sf/ commits" },
 	{ cmd: "add-tests", desc: "Generate tests for completed slices" },
+	{
+		cmd: "scaffold",
+		desc: "Inspect or refresh ADR-021 versioned scaffold docs (sync, --dry-run, --include-editing, --only=<glob>)",
+	},
 ];
 
 const NESTED_COMPLETIONS: CompletionMap = {
@@ -384,6 +388,21 @@ const NESTED_COMPLETIONS: CompletionMap = {
 		{ cmd: "--dry-run", desc: "Preview what would be filtered" },
 		{ cmd: "--name", desc: "Custom branch name" },
 	],
+	scaffold: [
+		{
+			cmd: "sync",
+			desc: "Refresh ADR-021 scaffold docs (drift report + apply pending upgrades)",
+		},
+		{ cmd: "sync --dry-run", desc: "Print drift report without modifying files" },
+		{
+			cmd: "sync --include-editing",
+			desc: "Run scaffold-keeper synchronously for editing-drift items",
+		},
+		{
+			cmd: "sync --only=",
+			desc: "Restrict the operation to a path glob (e.g. --only=harness/**)",
+		},
+	],
 };
 
 function filterOptions(
diff --git a/src/resources/extensions/sf/commands/handlers/ops.ts b/src/resources/extensions/sf/commands/handlers/ops.ts
index 73c8043f0..e299199e8 100644
--- a/src/resources/extensions/sf/commands/handlers/ops.ts
+++ b/src/resources/extensions/sf/commands/handlers/ops.ts
@@ -339,6 +339,23 @@ Examples:
 		await handleAddTests(trimmed.replace(/^add-tests\s*/, "").trim(), ctx, pi);
 		return true;
 	}
+	if (trimmed === "scaffold sync" || trimmed.startsWith("scaffold sync ")) {
+		const { handleScaffoldSync } = await import(
+			"../../commands-scaffold-sync.js"
+		);
+		await handleScaffoldSync(
+			trimmed.replace(/^scaffold sync\s*/, "").trim(),
+			ctx,
+		);
+		return true;
+	}
+	if (trimmed === "scaffold") {
+		ctx.ui.notify(
+			"Usage: /sf scaffold sync [--dry-run] [--include-editing] [--only=<glob>]",
+			"warning",
+		);
+		return true;
+	}
 	if (
 		trimmed === "extract-learnings" ||
 		trimmed.startsWith("extract-learnings ")
diff --git a/src/resources/extensions/sf/doctor-runtime-checks.ts b/src/resources/extensions/sf/doctor-runtime-checks.ts
index fa801a2a5..cf9844ca9 100644
--- a/src/resources/extensions/sf/doctor-runtime-checks.ts
+++ b/src/resources/extensions/sf/doctor-runtime-checks.ts
@@ -711,6 +711,66 @@ export async function checkRuntimeHealth(
 	} catch {
 		// Non-fatal — snapshot ref check failed
 	}
+
+	// ── Scaffold freshness (ADR-021 Phase C) ──────────────────────────────
+	// Visibility into scaffold drift. Phase C runs the silent path
+	// automatically on every SF startup, but the doctor finding lets users
+	// see what was upgraded and what is still pending review (editing-drift,
+	// untracked-without-archive-match). Severity: warning. Never blocks.
+	try {
+		const finding = checkScaffoldFreshness(basePath);
+		if (finding) issues.push(finding);
+	} catch {
+		// Non-fatal — scaffold freshness check failed
+	}
+}
+
+/**
+ * ADR-021 Phase C: report scaffold drift bucket counts as a doctor finding.
+ *
+ * Returns `null` when there is nothing actionable (everything is current or
+ * customised by intent). Otherwise returns a single warning summarising the
+ * bucket counts. The phrase "Run /sf scaffold sync" is forward-looking —
+ * Phase E adds the command. Phase C runs the silent path automatically on
+ * every SF startup, so the user does not need to act on most of these.
+ */
+export function checkScaffoldFreshness(basePath: string): DoctorIssue | null {
+	let report: ReturnType<typeof detectScaffoldDrift>;
+	try {
+		report = detectScaffoldDrift(basePath);
+	} catch {
+		return null;
+	}
+
+	const counts = report.countsByBucket;
+	const actionable =
+		counts.missing +
+		counts.upgradable +
+		counts["editing-drift"] +
+		counts.untracked;
+	if (actionable === 0) return null;
+
+	const parts: string[] = [];
+	if (counts.missing > 0) parts.push(`${counts.missing} missing`);
+	if (counts.upgradable > 0) parts.push(`${counts.upgradable} pending upgrade`);
+	if (counts["editing-drift"] > 0)
+		parts.push(`${counts["editing-drift"]} editing-drift`);
+	if (counts.untracked > 0) parts.push(`${counts.untracked} untracked`);
+
+	const summary = parts.join(", ");
+	const guidance =
+		counts.upgradable + counts.missing > 0
+			? `Run /sf scaffold sync to refresh ${counts.upgradable + counts.missing} pending docs`
+			: "Run /sf scaffold sync to inspect drift";
+
+	return {
+		severity: "warning",
+		code: "scaffold_drift",
+		scope: "project",
+		unitId: "project",
+		message: `Scaffold drift: ${summary}. ${guidance}.`,
+		fixable: false,
+	};
 }
 
 /**
diff --git a/src/resources/extensions/sf/scaffold-keeper.ts b/src/resources/extensions/sf/scaffold-keeper.ts
new file mode 100644
index 000000000..509868485
--- /dev/null
+++ b/src/resources/extensions/sf/scaffold-keeper.ts
@@ -0,0 +1,184 @@
+/**
+ * Scaffold-keeper background dispatcher (ADR-021 Phase D).
+ *
+ * Runs after milestone completion (and any other place SF chooses to call it).
+ * Walks the drift report, and for every `editing-drift` item produces a
+ * `<file>.proposed` artifact and emits a single structured `approval_request`
+ * notification so the user can review the proposal.
+ *
+ * Phase D ships the architecture and a deterministic stub for the proposed
+ * body: the current scaffold template content with a `<!-- sf-proposed: ... -->`
+ * preamble. A follow-up phase will replace the body generator with a real
+ * subagent dispatch that runs the `records-keeper` skill — at that point the
+ * `<file>.proposed` body will be code-derived (records-keeper's "prefer source
+ * and tests for implemented behavior" contract) instead of template-only.
+ *
+ * Contract:
+ *   - Non-blocking. Caller does not await the body. Failures are non-fatal:
+ *     they log via `logWarning("scaffold", ...)` and never propagate.
+ *   - Never overwrites `<file>` itself — only writes `<file>.proposed`.
+ *   - Emits exactly one `approval_request` notification per call when there is
+ *     at least one editing-drift item; the stable `dedupe_key` prevents the
+ *     same drift from spamming the user across repeated runs.
+ *   - Silent path: when there are zero editing-drift items, no notification,
+ *     no .proposed writes, no logs.
+ */
+import { existsSync, mkdirSync, writeFileSync } from "node:fs";
+import { dirname, join } from "node:path";
+
+import { SCAFFOLD_FILES } from "./agentic-docs-scaffold.js";
+import { detectScaffoldDrift } from "./scaffold-drift.js";
+import type { ScaffoldDriftItem } from "./scaffold-drift.js";
+import { logWarning } from "./workflow-logger.js";
+
+/**
+ * Minimal `notify`-only shape of `ExtensionContext`. Tests pass a stub; the
+ * real auto loop passes the full context. Keeping this typed locally avoids
+ * pulling the heavy `@singularity-forge/pi-coding-agent` import surface into a
+ * module that runs at session edges.
+ */
+export interface ScaffoldKeeperCtx {
+	ui: {
+		notify: (
+			message: string,
+			type?: "info" | "warning" | "error" | "success",
+			metadata?: {
+				kind?: "notice" | "approval_request" | "progress" | "terminal";
+				blocking?: boolean;
+				dedupe_key?: string;
+				source?: string;
+			},
+		) => void;
+	};
+}
+
+/**
+ * Build the .proposed body shipped by the Phase-D stub: the current scaffold
+ * template body, prefixed with a structured `<!-- sf-proposed: ... -->` block
+ * describing source vs target version. This matches ADR-021 §5 ("editing-drift").
+ *
+ * The records-keeper skill is referenced in the preamble so a human reviewing
+ * the artifact knows which skill the agent will run when wired up.
+ */
+function buildProposedBody(item: ScaffoldDriftItem, templateBody: string): string {
+	const sourceVersion = item.currentVersion ?? "unknown";
+	const targetVersion = item.shipVersion;
+	const preamble =
+		`<!-- sf-proposed: source=${sourceVersion} target=${targetVersion} ` +
+		`template=${item.template} skill=records-keeper ` +
+		`note="Stub body — replace with code-derived content via records-keeper subagent." ` +
+		`-->\n`;
+	return preamble + templateBody;
+}
+
+/**
+ * Scaffold-keeper entry point. Fire-and-forget — caller should not await
+ * meaningful work, only the inevitable I/O completion.
+ *
+ * Steps:
+ *   1. detect drift; bail silently if no editing-drift items.
+ *   2. for each editing-drift item, write `<file>.proposed` with the stub
+ *      body. Skip files with no matching `SCAFFOLD_FILES` entry (defensive).
+ *   3. emit a single `approval_request` notification summarizing the count.
+ *
+ * Returns the number of `.proposed` files written. Tests use this to assert
+ * the smoke-check behaviour; production callers ignore the return value.
+ */
+export async function dispatchScaffoldKeeperIfNeeded(
+	basePath: string,
+	ctx: ScaffoldKeeperCtx,
+): Promise<number> {
+	let report: ReturnType<typeof detectScaffoldDrift>;
+	try {
+		report = detectScaffoldDrift(basePath);
+	} catch (err) {
+		logWarning("scaffold", "scaffold-keeper drift detection failed", {
+			error: (err as Error).message,
+		});
+		return 0;
+	}
+
+	if (report.countsByBucket["editing-drift"] === 0) {
+		return 0;
+	}
+
+	const editingDrift = report.items.filter((i) => i.bucket === "editing-drift");
+	let written = 0;
+
+	for (const item of editingDrift) {
+		try {
+			const template = SCAFFOLD_FILES.find((f) => f.path === item.template);
+			if (!template) {
+				logWarning("scaffold", "scaffold-keeper: no template for drift item", {
+					path: item.path,
+				});
+				continue;
+			}
+			const proposedPath = join(basePath, `${item.path}.proposed`);
+			const proposedBody = buildProposedBody(item, template.content);
+			mkdirSync(dirname(proposedPath), { recursive: true });
+			writeFileSync(proposedPath, proposedBody, "utf-8");
+			written += 1;
+		} catch (err) {
+			logWarning("scaffold", "scaffold-keeper: failed to write .proposed", {
+				path: item.path,
+				error: (err as Error).message,
+			});
+		}
+	}
+
+	// Stub notice — when subagent dispatch is wired, this log line goes away
+	// and the body becomes code-derived rather than template-only.
+	logWarning(
+		"scaffold",
+		"scaffold-keeper agent dispatch not yet wired — wrote .proposed with template only",
+		{ count: String(written) },
+	);
+
+	if (written > 0) {
+		try {
+			ctx.ui.notify(
+				`Scaffold drift: ${written} doc(s) need review. See .proposed files.`,
+				"warning",
+				{
+					kind: "approval_request",
+					blocking: false,
+					dedupe_key: "scaffold-drift",
+					source: "scaffold-keeper",
+				},
+			);
+		} catch (err) {
+			logWarning("scaffold", "scaffold-keeper: notify failed", {
+				error: (err as Error).message,
+			});
+		}
+	}
+
+	return written;
+}
+
+/**
+ * Sync wrapper: schedules `dispatchScaffoldKeeperIfNeeded` without blocking the
+ * caller. Errors swallowed and logged so a scaffold-keeper failure cannot break
+ * the auto loop. Used from auto-post-unit and auto.ts:stopAuto where the
+ * caller cannot reasonably `await` async work without re-architecting cleanup.
+ */
+export function dispatchScaffoldKeeperFireAndForget(
+	basePath: string,
+	ctx: ScaffoldKeeperCtx,
+): void {
+	// Use queueMicrotask so the dispatch starts after the current sync stack
+	// unwinds — the caller's flow remains synchronous and unblocked.
+	queueMicrotask(() => {
+		dispatchScaffoldKeeperIfNeeded(basePath, ctx).catch((err: unknown) => {
+			logWarning("scaffold", "scaffold-keeper dispatch threw", {
+				error: err instanceof Error ? err.message : String(err),
+			});
+		});
+	});
+}
+
+// Test-only helper: not exported via index, but exposed for the smoke test.
+export const __test = {
+	buildProposedBody,
+};
diff --git a/src/resources/extensions/sf/tests/scaffold-keeper.test.ts b/src/resources/extensions/sf/tests/scaffold-keeper.test.ts
new file mode 100644
index 000000000..5b3a947da
--- /dev/null
+++ b/src/resources/extensions/sf/tests/scaffold-keeper.test.ts
@@ -0,0 +1,201 @@
+/**
+ * Tests for scaffold-keeper (ADR-021 Phase D).
+ *
+ * Covers the four observable behaviors:
+ *   1. editing-drift produces a .proposed file and one notification
+ *   2. silent path: no editing-drift → no notification, no .proposed writes
+ *   3. failures inside the dispatcher do not throw to the caller
+ *   4. completed/pending state files do not trigger the dispatcher
+ */
+import assert from "node:assert/strict";
+import {
+	existsSync,
+	mkdtempSync,
+	readFileSync,
+	rmSync,
+	writeFileSync,
+} from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, beforeEach, describe, test } from "node:test";
+
+import { SCAFFOLD_FILES } from "../agentic-docs-scaffold.ts";
+import { dispatchScaffoldKeeperIfNeeded } from "../scaffold-keeper.ts";
+import { stampScaffoldFile } from "../scaffold-versioning.ts";
+
+interface NotifyCall {
+	message: string;
+	type?: string;
+	metadata?: Record<string, unknown>;
+}
+
+function makeStubCtx(): { ctx: { ui: { notify: (...args: unknown[]) => void } }; calls: NotifyCall[] } {
+	const calls: NotifyCall[] = [];
+	const ctx = {
+		ui: {
+			notify: (
+				message: string,
+				type?: string,
+				metadata?: Record<string, unknown>,
+			) => {
+				calls.push({ message, type, metadata });
+			},
+		},
+	};
+	return { ctx, calls };
+}
+
+function makeTmp(): string {
+	return mkdtempSync(join(tmpdir(), "sf-scaffold-keeper-"));
+}
+
+function pickMarkdownTarget(): { path: string; content: string } {
+	const f = SCAFFOLD_FILES.find((s) => s.path === "AGENTS.md");
+	if (!f) throw new Error("AGENTS.md must be in SCAFFOLD_FILES for this test");
+	return { path: f.path, content: f.content };
+}
+
+/**
+ * Set up a file in editing-drift state: stamped marker, then body mutated.
+ */
+function makeEditingDrift(dir: string): string {
+	const target = pickMarkdownTarget();
+	const fp = join(dir, target.path);
+	writeFileSync(fp, target.content, "utf-8");
+	stampScaffoldFile(fp, target.path, "1.0.0");
+	const stamped = readFileSync(fp, "utf-8");
+	const lines = stamped.split("\n");
+	const mutated =
+		lines[0] + "\n" + lines.slice(1).join("\n") + "\n# user customisation\n";
+	writeFileSync(fp, mutated, "utf-8");
+	return fp;
+}
+
+describe("dispatchScaffoldKeeperIfNeeded", () => {
+	let dir: string;
+	beforeEach(() => {
+		dir = makeTmp();
+	});
+	afterEach(() => {
+		rmSync(dir, { recursive: true, force: true });
+	});
+
+	test("editing-drift produces .proposed file and one notification", async () => {
+		makeEditingDrift(dir);
+		const { ctx, calls } = makeStubCtx();
+
+		const written = await dispatchScaffoldKeeperIfNeeded(dir, ctx);
+
+		assert.equal(written, 1);
+		const proposedPath = join(dir, "AGENTS.md.proposed");
+		assert.ok(existsSync(proposedPath), ".proposed file must exist");
+		const body = readFileSync(proposedPath, "utf-8");
+		assert.match(body, /<!-- sf-proposed:/);
+		assert.match(body, /skill=records-keeper/);
+
+		assert.equal(calls.length, 1);
+		assert.equal(calls[0].type, "warning");
+		assert.equal(calls[0].metadata?.kind, "approval_request");
+		assert.equal(calls[0].metadata?.dedupe_key, "scaffold-drift");
+		assert.equal(calls[0].metadata?.source, "scaffold-keeper");
+		assert.equal(calls[0].metadata?.blocking, false);
+	});
+
+	test("never overwrites the original file", async () => {
+		const fp = makeEditingDrift(dir);
+		const before = readFileSync(fp, "utf-8");
+		const { ctx } = makeStubCtx();
+
+		await dispatchScaffoldKeeperIfNeeded(dir, ctx);
+
+		const after = readFileSync(fp, "utf-8");
+		assert.equal(after, before, "original file must be untouched");
+	});
+
+	test("silent path: no editing-drift means no notification and no .proposed", async () => {
+		// All scaffold files are missing → all classified as `missing`, none as
+		// `editing-drift`. No notification, no .proposed files.
+		const { ctx, calls } = makeStubCtx();
+
+		const written = await dispatchScaffoldKeeperIfNeeded(dir, ctx);
+
+		assert.equal(written, 0);
+		assert.equal(calls.length, 0);
+	});
+
+	test("dedupe_key is stable across repeated invocations", async () => {
+		makeEditingDrift(dir);
+		const { ctx, calls } = makeStubCtx();
+
+		await dispatchScaffoldKeeperIfNeeded(dir, ctx);
+		await dispatchScaffoldKeeperIfNeeded(dir, ctx);
+
+		// Both calls should fire the notification with the same dedupe_key.
+		// Deduplication is the consumer's job; the keeper's contract is "stable
+		// key" so the consumer can collapse them.
+		assert.equal(calls.length, 2);
+		assert.equal(calls[0].metadata?.dedupe_key, "scaffold-drift");
+		assert.equal(calls[1].metadata?.dedupe_key, "scaffold-drift");
+	});
+
+	test("completed marker does not trigger dispatch", async () => {
+		const target = pickMarkdownTarget();
+		const fp = join(dir, target.path);
+		writeFileSync(fp, target.content, "utf-8");
+		stampScaffoldFile(fp, target.path, "1.0.0", "completed");
+
+		const { ctx, calls } = makeStubCtx();
+
+		const written = await dispatchScaffoldKeeperIfNeeded(dir, ctx);
+
+		assert.equal(written, 0);
+		assert.equal(calls.length, 0);
+		assert.ok(!existsSync(join(dir, "AGENTS.md.proposed")));
+	});
+
+	test("pending (not drifted) does not trigger dispatch", async () => {
+		const target = pickMarkdownTarget();
+		const fp = join(dir, target.path);
+		writeFileSync(fp, target.content, "utf-8");
+		// Stamp current SF_VERSION → bucket is `customized`/`upgradable`, never editing-drift.
+		stampScaffoldFile(fp, target.path, process.env.SF_VERSION || "0.0.0");
+
+		const { ctx, calls } = makeStubCtx();
+
+		const written = await dispatchScaffoldKeeperIfNeeded(dir, ctx);
+
+		assert.equal(written, 0);
+		assert.equal(calls.length, 0);
+		assert.ok(!existsSync(join(dir, "AGENTS.md.proposed")));
+	});
+
+	test("notify failure inside dispatcher does not throw to caller", async () => {
+		makeEditingDrift(dir);
+		const ctx = {
+			ui: {
+				notify: () => {
+					throw new Error("notify exploded");
+				},
+			},
+		};
+
+		// Must not throw despite notify throwing.
+		const written = await dispatchScaffoldKeeperIfNeeded(dir, ctx);
+		assert.equal(written, 1);
+		assert.ok(existsSync(join(dir, "AGENTS.md.proposed")));
+	});
+
+	test("smoke check — full happy-path workflow", async () => {
+		// Mirrors the ADR's verification step: stamp a file, mutate the body,
+		// run the keeper, assert .proposed exists and notify was called once.
+		const fp = makeEditingDrift(dir);
+		assert.ok(existsSync(fp));
+
+		const { ctx, calls } = makeStubCtx();
+		const written = await dispatchScaffoldKeeperIfNeeded(dir, ctx);
+
+		assert.equal(written, 1);
+		assert.equal(calls.length, 1);
+		assert.ok(existsSync(join(dir, "AGENTS.md.proposed")));
+	});
+});