diff --git a/src/resources/extensions/gsd/commands-extract-learnings.ts b/src/resources/extensions/gsd/commands-extract-learnings.ts
new file mode 100644
index 000000000..634cb3936
--- /dev/null
+++ b/src/resources/extensions/gsd/commands-extract-learnings.ts
@@ -0,0 +1,296 @@
+/**
+ * GSD Command — /gsd extract-learnings
+ *
+ * Analyses completed milestone artefacts and dispatches an LLM turn that
+ * extracts structured knowledge into 4 categories:
+ *   Decisions · Lessons · Patterns · Surprises
+ */
+
+import type { ExtensionAPI, ExtensionCommandContext } from "@gsd/pi-coding-agent";
+
+import { existsSync, readFileSync } from "node:fs";
+import { join, basename } from "node:path";
+
+import { gsdRoot, resolveMilestonePath } from "./paths.js";
+import { projectRoot } from "./commands/context.js";
+
+// ─── Types ────────────────────────────────────────────────────────────────────
+
+export interface PhaseArtifacts {
+  plan: string | null;
+  summary: string | null;
+  verification: string | null;
+  uat: string | null;
+  missingRequired: string[];
+}
+
+export interface ExtractLearningsPromptContext {
+  milestoneId: string;
+  milestoneName: string;
+  outputPath: string;
+  relativeOutputPath: string;
+  planContent: string;
+  summaryContent: string;
+  verificationContent: string | null;
+  uatContent: string | null;
+  missingArtifacts: string[];
+  projectName: string;
+}
+
+export interface FrontmatterContext {
+  milestoneId: string;
+  milestoneName: string;
+  projectName: string;
+  generatedAt: string;
+  counts: {
+    decisions: number;
+    lessons: number;
+    patterns: number;
+    surprises: number;
+  };
+  missingArtifacts: string[];
+}
+
+// ─── Pure functions ───────────────────────────────────────────────────────────
+
+export function parseExtractLearningsArgs(args: string): { milestoneId: string | null } {
+  const trimmed = args.trim();
+  return { milestoneId: trimmed || null };
+}
+
+export function buildLearningsOutputPath(milestoneDir: string, milestoneId: string): string {
+  return join(milestoneDir, `${milestoneId}-LEARNINGS.md`);
+}
+
+export function resolvePhaseArtifacts(milestoneDir: string, milestoneId: string): PhaseArtifacts {
+  const missingRequired: string[] = [];
+
+  const planFile = `${milestoneId}-PLAN.md`;
+  const summaryFile = `${milestoneId}-SUMMARY.md`;
+  const verificationFile = `${milestoneId}-VERIFICATION.md`;
+  const uatFile = `${milestoneId}-UAT.md`;
+
+  const planPath = join(milestoneDir, planFile);
+  const summaryPath = join(milestoneDir, summaryFile);
+  const verificationPath = join(milestoneDir, verificationFile);
+  const uatPath = join(milestoneDir, uatFile);
+
+  const plan = existsSync(planPath) ? planPath : null;
+  const summary = existsSync(summaryPath) ? summaryPath : null;
+  const verification = existsSync(verificationPath) ? verificationPath : null;
+  const uat = existsSync(uatPath) ? uatPath : null;
+
+  if (!plan) missingRequired.push(planFile);
+  if (!summary) missingRequired.push(summaryFile);
+
+  return { plan, summary, verification, uat, missingRequired };
+}
+
+export function buildExtractLearningsPrompt(ctx: ExtractLearningsPromptContext): string {
+  const optionalSections: string[] = [];
+
+  if (ctx.verificationContent) {
+    optionalSections.push(`## Verification Report\n\n${ctx.verificationContent}`);
+  }
+  if (ctx.uatContent) {
+    optionalSections.push(`## UAT Report\n\n${ctx.uatContent}`);
+  }
+
+  const missingNote = ctx.missingArtifacts.length > 0
+    ? `\nNote: The following optional artefacts were not available: ${ctx.missingArtifacts.join(", ")}\n`
+    : "";
+
+  return `# Extract Learnings — ${ctx.milestoneId}: ${ctx.milestoneName}
+
+**Project:** ${ctx.projectName}
+**Output file:** ${ctx.outputPath}
+
+## Your Task
+
+Analyse the artefacts below and extract structured knowledge from milestone **${ctx.milestoneId}**.
+
+Write a LEARNINGS document to \`${ctx.outputPath}\` with the following 4 sections:
+
+### Decisions
+Key architectural and design decisions made during this milestone, including the rationale and alternatives considered.
+
+### Lessons
+What the team learned — technical discoveries, process insights, and knowledge gaps that were filled.
+
+### Patterns
+Reusable patterns, approaches, or solutions that emerged and should be applied in future work.
+
+### Surprises
+Unexpected challenges, discoveries, or outcomes — things that deviated from assumptions.
+
+### Source Attribution (REQUIRED)
+
+Every extracted item MUST include a \`Source:\` line immediately after the item text.
+Format: \`Source: {artifact-filename}/{section}\`
+Example: \`Source: M001-PLAN.md/Architecture Decisions\`
+
+Items without a Source attribution are invalid and must not be included in the output.
+
+---
+
+## Artefacts
+
+### Plan
+
+${ctx.planContent}
+
+---
+
+### Summary
+
+${ctx.summaryContent}
+
+${optionalSections.join("\n\n---\n\n")}
+${missingNote}
+---
+
+## Output Format
+
+Write the LEARNINGS file to \`${ctx.relativeOutputPath}\` with YAML frontmatter followed by the 4 sections above.
+Each section should contain concise, actionable bullet points.
+Every bullet point MUST be followed by a source line, for example:
+
+\`\`\`
+### Decisions
+- Chose PostgreSQL over SQLite for concurrent write support.
+  Source: M001-PLAN.md/Architecture Decisions
+\`\`\`
+
+Items without a \`Source:\` line are invalid.
+
+---
+
+## Optional: Capture Individual Learnings
+
+If the \`capture_thought\` tool is available, call it once for each extracted item with:
+- category: "decision" | "lesson" | "pattern" | "surprise"
+- phase: "${ctx.milestoneId}"
+- content: {the learning text}
+- source: {artifact filename}
+
+If \`capture_thought\` is not available, skip this step silently — do not report an error.
+`;
+}
+
+export function buildFrontmatter(ctx: FrontmatterContext): string {
+  const missingList = ctx.missingArtifacts.length > 0
+    ? ctx.missingArtifacts.map((a) => `  - ${a}`).join("\n")
+    : "  []";
+
+  const missingValue = ctx.missingArtifacts.length > 0
+    ? `\n${missingList}`
+    : " []";
+
+  return `---
+phase: ${ctx.milestoneId}
+phase_name: ${ctx.milestoneName}
+project: ${ctx.projectName}
+generated: ${ctx.generatedAt}
+counts:
+  decisions: ${ctx.counts.decisions}
+  lessons: ${ctx.counts.lessons}
+  patterns: ${ctx.counts.patterns}
+  surprises: ${ctx.counts.surprises}
+missing_artifacts:${missingValue}
+---`;
+}
+
+export function extractProjectName(basePath: string): string {
+  const projectMdPath = join(gsdRoot(basePath), "PROJECT.md");
+
+  if (existsSync(projectMdPath)) {
+    try {
+      const content = readFileSync(projectMdPath, "utf-8");
+      const match = content.match(/^name:\s*(.+)$/m);
+      if (match) return match[1].trim();
+    } catch {
+      // non-fatal
+    }
+  }
+
+  return basename(basePath);
+}
+
+// ─── Handler ──────────────────────────────────────────────────────────────────
+
+export async function handleExtractLearnings(
+  args: string,
+  ctx: ExtensionCommandContext,
+  pi: ExtensionAPI,
+): Promise<void> {
+  const { milestoneId } = parseExtractLearningsArgs(args);
+
+  if (!milestoneId) {
+    ctx.ui.notify("Usage: /gsd extract-learnings <milestoneId>  (e.g. M001)", "warning");
+    return;
+  }
+
+  // projectRoot() throws GSDNoProjectError if no project found — intentional, handled by dispatcher
+  const basePath = projectRoot();
+  const milestoneDir = resolveMilestonePath(basePath, milestoneId);
+
+  if (!milestoneDir) {
+    ctx.ui.notify(`Milestone not found: ${milestoneId}`, "error");
+    return;
+  }
+
+  const artifacts = resolvePhaseArtifacts(milestoneDir, milestoneId);
+
+  if (artifacts.missingRequired.length > 0) {
+    ctx.ui.notify(
+      `Cannot extract learnings — required artefacts missing: ${artifacts.missingRequired.join(", ")}`,
+      "error",
+    );
+    return;
+  }
+
+  // Read required artefacts
+  const planContent = readFileSync(artifacts.plan!, "utf-8");
+  const summaryContent = readFileSync(artifacts.summary!, "utf-8");
+
+  // Read optional artefacts
+  const verificationContent = artifacts.verification
+    ? readFileSync(artifacts.verification, "utf-8")
+    : null;
+  const uatContent = artifacts.uat
+    ? readFileSync(artifacts.uat, "utf-8")
+    : null;
+
+  // Determine missing optional artefacts for context
+  const missingArtifacts: string[] = [];
+  if (!artifacts.verification) missingArtifacts.push(`${milestoneId}-VERIFICATION.md`);
+  if (!artifacts.uat) missingArtifacts.push(`${milestoneId}-UAT.md`);
+
+  // Extract milestone name from Plan H1 or fall back to milestoneId
+  const h1Match = planContent.match(/^#\s+(.+)$/m);
+  const milestoneName = h1Match?.[1]?.trim() ?? milestoneId;
+
+  const projectName = extractProjectName(basePath);
+  const outputPath = buildLearningsOutputPath(milestoneDir, milestoneId);
+  const relativeOutputPath = outputPath.replace(basePath + "/", "");
+
+  const prompt = buildExtractLearningsPrompt({
+    milestoneId,
+    milestoneName,
+    outputPath,
+    relativeOutputPath,
+    planContent,
+    summaryContent,
+    verificationContent,
+    uatContent,
+    missingArtifacts,
+    projectName,
+  });
+
+  ctx.ui.notify(`Extracting learnings for ${milestoneId}: "${milestoneName}"...`, "info");
+
+  pi.sendMessage(
+    { customType: "gsd-extract-learnings", content: prompt, display: false },
+    { triggerTurn: true },
+  );
+}
diff --git a/src/resources/extensions/gsd/commands/handlers/ops.ts b/src/resources/extensions/gsd/commands/handlers/ops.ts
index 2e584b117..3a8a2fe19 100644
--- a/src/resources/extensions/gsd/commands/handlers/ops.ts
+++ b/src/resources/extensions/gsd/commands/handlers/ops.ts
@@ -236,5 +236,10 @@ Examples:
     await handleAddTests(trimmed.replace(/^add-tests\s*/, "").trim(), ctx, pi);
     return true;
   }
+  if (trimmed === "extract-learnings" || trimmed.startsWith("extract-learnings ")) {
+    const { handleExtractLearnings } = await import("../../commands-extract-learnings.js");
+    await handleExtractLearnings(trimmed.replace(/^extract-learnings\s*/, "").trim(), ctx, pi);
+    return true;
+  }
   return false;
 }
diff --git a/src/resources/extensions/gsd/tests/commands-extract-learnings.test.ts b/src/resources/extensions/gsd/tests/commands-extract-learnings.test.ts
new file mode 100644
index 000000000..de148c7d5
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/commands-extract-learnings.test.ts
@@ -0,0 +1,340 @@
+import { describe, it, beforeEach, afterEach } from "node:test";
+import assert from "node:assert/strict";
+import { mkdirSync, writeFileSync, rmSync } from "node:fs";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+import { randomUUID } from "node:crypto";
+
+import {
+  parseExtractLearningsArgs,
+  buildLearningsOutputPath,
+  resolvePhaseArtifacts,
+  buildExtractLearningsPrompt,
+  buildFrontmatter,
+  extractProjectName,
+} from "../commands-extract-learnings.js";
+
+// ─── parseExtractLearningsArgs ────────────────────────────────────────────────
+
+describe("parseExtractLearningsArgs", () => {
+  it("parses a milestone ID", () => {
+    const result = parseExtractLearningsArgs("M001");
+    assert.deepEqual(result, { milestoneId: "M001" });
+  });
+
+  it("returns null milestoneId for empty string", () => {
+    const result = parseExtractLearningsArgs("");
+    assert.deepEqual(result, { milestoneId: null });
+  });
+
+  it("returns null milestoneId for whitespace-only string", () => {
+    const result = parseExtractLearningsArgs("  ");
+    assert.deepEqual(result, { milestoneId: null });
+  });
+
+  it("trims whitespace from milestone ID", () => {
+    const result = parseExtractLearningsArgs("  M002  ");
+    assert.deepEqual(result, { milestoneId: "M002" });
+  });
+});
+
+// ─── buildLearningsOutputPath ─────────────────────────────────────────────────
+
+describe("buildLearningsOutputPath", () => {
+  it("builds the correct output path", () => {
+    const result = buildLearningsOutputPath("/base/.gsd/milestones/M001", "M001");
+    assert.equal(result, "/base/.gsd/milestones/M001/M001-LEARNINGS.md");
+  });
+
+  it("builds path for different milestone ID", () => {
+    const result = buildLearningsOutputPath("/project/.gsd/milestones/M005", "M005");
+    assert.equal(result, "/project/.gsd/milestones/M005/M005-LEARNINGS.md");
+  });
+});
+
+// ─── resolvePhaseArtifacts ────────────────────────────────────────────────────
+
+describe("resolvePhaseArtifacts", () => {
+  let tmpBase: string;
+
+  beforeEach(() => {
+    tmpBase = join(tmpdir(), `gsd-learnings-test-${randomUUID()}`);
+    mkdirSync(tmpBase, { recursive: true });
+  });
+
+  afterEach(() => {
+    rmSync(tmpBase, { recursive: true, force: true });
+  });
+
+  it("finds required PLAN and SUMMARY when both present", () => {
+    writeFileSync(join(tmpBase, "M001-PLAN.md"), "# M001 Plan content", "utf-8");
+    writeFileSync(join(tmpBase, "M001-SUMMARY.md"), "# M001 Summary content", "utf-8");
+
+    const result = resolvePhaseArtifacts(tmpBase, "M001");
+    assert.equal(result.plan, join(tmpBase, "M001-PLAN.md"));
+    assert.equal(result.summary, join(tmpBase, "M001-SUMMARY.md"));
+    assert.deepEqual(result.missingRequired, []);
+  });
+
+  it("reports missing PLAN as missingRequired", () => {
+    writeFileSync(join(tmpBase, "M001-SUMMARY.md"), "# Summary", "utf-8");
+
+    const result = resolvePhaseArtifacts(tmpBase, "M001");
+    assert.ok(result.missingRequired.includes("M001-PLAN.md"));
+    assert.equal(result.plan, null);
+  });
+
+  it("reports missing SUMMARY as missingRequired", () => {
+    writeFileSync(join(tmpBase, "M001-PLAN.md"), "# Plan", "utf-8");
+
+    const result = resolvePhaseArtifacts(tmpBase, "M001");
+    assert.ok(result.missingRequired.includes("M001-SUMMARY.md"));
+    assert.equal(result.summary, null);
+  });
+
+  it("reports both required files missing when neither present", () => {
+    const result = resolvePhaseArtifacts(tmpBase, "M001");
+    assert.equal(result.missingRequired.length, 2);
+    assert.ok(result.missingRequired.includes("M001-PLAN.md"));
+    assert.ok(result.missingRequired.includes("M001-SUMMARY.md"));
+  });
+
+  it("finds optional VERIFICATION when present", () => {
+    writeFileSync(join(tmpBase, "M001-PLAN.md"), "# Plan", "utf-8");
+    writeFileSync(join(tmpBase, "M001-SUMMARY.md"), "# Summary", "utf-8");
+    writeFileSync(join(tmpBase, "M001-VERIFICATION.md"), "# Verification", "utf-8");
+
+    const result = resolvePhaseArtifacts(tmpBase, "M001");
+    assert.equal(result.verification, join(tmpBase, "M001-VERIFICATION.md"));
+  });
+
+  it("returns null for optional VERIFICATION when absent", () => {
+    writeFileSync(join(tmpBase, "M001-PLAN.md"), "# Plan", "utf-8");
+    writeFileSync(join(tmpBase, "M001-SUMMARY.md"), "# Summary", "utf-8");
+
+    const result = resolvePhaseArtifacts(tmpBase, "M001");
+    assert.equal(result.verification, null);
+  });
+
+  it("finds optional UAT when present", () => {
+    writeFileSync(join(tmpBase, "M001-PLAN.md"), "# Plan", "utf-8");
+    writeFileSync(join(tmpBase, "M001-SUMMARY.md"), "# Summary", "utf-8");
+    writeFileSync(join(tmpBase, "M001-UAT.md"), "# UAT", "utf-8");
+
+    const result = resolvePhaseArtifacts(tmpBase, "M001");
+    assert.equal(result.uat, join(tmpBase, "M001-UAT.md"));
+  });
+
+  it("returns null for optional UAT when absent, no error", () => {
+    writeFileSync(join(tmpBase, "M001-PLAN.md"), "# Plan", "utf-8");
+    writeFileSync(join(tmpBase, "M001-SUMMARY.md"), "# Summary", "utf-8");
+
+    const result = resolvePhaseArtifacts(tmpBase, "M001");
+    assert.equal(result.uat, null);
+    assert.deepEqual(result.missingRequired, []);
+  });
+});
+
+// ─── buildExtractLearningsPrompt ──────────────────────────────────────────────
+
+describe("buildExtractLearningsPrompt", () => {
+  it("includes milestoneId and outputPath", () => {
+    const result = buildExtractLearningsPrompt({
+      milestoneId: "M001",
+      milestoneName: "Test Milestone",
+      outputPath: "/project/.gsd/milestones/M001/M001-LEARNINGS.md",
+      relativeOutputPath: ".gsd/milestones/M001/M001-LEARNINGS.md",
+      planContent: "# Plan content",
+      summaryContent: "# Summary content",
+      verificationContent: null,
+      uatContent: null,
+      missingArtifacts: [],
+      projectName: "MyProject",
+    });
+
+    assert.ok(result.includes("M001"));
+    assert.ok(result.includes("/project/.gsd/milestones/M001/M001-LEARNINGS.md"));
+  });
+
+  it("includes all 4 learning categories", () => {
+    const result = buildExtractLearningsPrompt({
+      milestoneId: "M001",
+      milestoneName: "Test Milestone",
+      outputPath: "/out/M001-LEARNINGS.md",
+      relativeOutputPath: ".gsd/milestones/M001/M001-LEARNINGS.md",
+      planContent: "# Plan",
+      summaryContent: "# Summary",
+      verificationContent: null,
+      uatContent: null,
+      missingArtifacts: [],
+      projectName: "MyProject",
+    });
+
+    assert.ok(result.includes("Decisions"));
+    assert.ok(result.includes("Lessons"));
+    assert.ok(result.includes("Patterns"));
+    assert.ok(result.includes("Surprises"));
+  });
+
+  it("includes plan and summary content", () => {
+    const result = buildExtractLearningsPrompt({
+      milestoneId: "M001",
+      milestoneName: "Test Milestone",
+      outputPath: "/out/M001-LEARNINGS.md",
+      relativeOutputPath: ".gsd/milestones/M001/M001-LEARNINGS.md",
+      planContent: "PLAN_CONTENT_UNIQUE_123",
+      summaryContent: "SUMMARY_CONTENT_UNIQUE_456",
+      verificationContent: null,
+      uatContent: null,
+      missingArtifacts: [],
+      projectName: "MyProject",
+    });
+
+    assert.ok(result.includes("PLAN_CONTENT_UNIQUE_123"));
+    assert.ok(result.includes("SUMMARY_CONTENT_UNIQUE_456"));
+  });
+
+  it("includes optional artifacts when present", () => {
+    const result = buildExtractLearningsPrompt({
+      milestoneId: "M001",
+      milestoneName: "Test Milestone",
+      outputPath: "/out/M001-LEARNINGS.md",
+      relativeOutputPath: ".gsd/milestones/M001/M001-LEARNINGS.md",
+      planContent: "# Plan",
+      summaryContent: "# Summary",
+      verificationContent: "VERIFICATION_UNIQUE_789",
+      uatContent: "UAT_UNIQUE_012",
+      missingArtifacts: [],
+      projectName: "MyProject",
+    });
+
+    assert.ok(result.includes("VERIFICATION_UNIQUE_789"));
+    assert.ok(result.includes("UAT_UNIQUE_012"));
+  });
+
+  it("lists missing artifacts when present", () => {
+    const result = buildExtractLearningsPrompt({
+      milestoneId: "M001",
+      milestoneName: "Test Milestone",
+      outputPath: "/out/M001-LEARNINGS.md",
+      relativeOutputPath: ".gsd/milestones/M001/M001-LEARNINGS.md",
+      planContent: "# Plan",
+      summaryContent: "# Summary",
+      verificationContent: null,
+      uatContent: null,
+      missingArtifacts: ["M001-VERIFICATION.md"],
+      projectName: "MyProject",
+    });
+
+    assert.ok(result.includes("M001-VERIFICATION.md"));
+  });
+});
+
+// ─── buildFrontmatter ─────────────────────────────────────────────────────────
+
+describe("buildFrontmatter", () => {
+  it("starts with --- and ends with ---", () => {
+    const result = buildFrontmatter({
+      milestoneId: "M001",
+      milestoneName: "Test Milestone",
+      projectName: "MyProject",
+      generatedAt: "2026-04-15T10:00:00Z",
+      counts: { decisions: 0, lessons: 0, patterns: 0, surprises: 0 },
+      missingArtifacts: [],
+    });
+
+    assert.ok(result.startsWith("---\n"));
+    assert.ok(result.endsWith("---"));
+  });
+
+  it("includes required fields", () => {
+    const result = buildFrontmatter({
+      milestoneId: "M001",
+      milestoneName: "Test Milestone",
+      projectName: "MyProject",
+      generatedAt: "2026-04-15T10:00:00Z",
+      counts: { decisions: 3, lessons: 2, patterns: 1, surprises: 0 },
+      missingArtifacts: [],
+    });
+
+    assert.ok(result.includes("phase:"));
+    assert.ok(result.includes("phase_name:"));
+    assert.ok(result.includes("project:"));
+    assert.ok(result.includes("generated:"));
+    assert.ok(result.includes("counts:"));
+    assert.ok(result.includes("missing_artifacts:"));
+  });
+
+  it("includes milestoneId as phase value", () => {
+    const result = buildFrontmatter({
+      milestoneId: "M001",
+      milestoneName: "Auth System",
+      projectName: "MyApp",
+      generatedAt: "2026-04-15T10:00:00Z",
+      counts: { decisions: 0, lessons: 0, patterns: 0, surprises: 0 },
+      missingArtifacts: [],
+    });
+
+    assert.ok(result.includes("M001"));
+    assert.ok(result.includes("Auth System"));
+    assert.ok(result.includes("MyApp"));
+    assert.ok(result.includes("2026-04-15T10:00:00Z"));
+  });
+
+  it("includes missing artifacts list", () => {
+    const result = buildFrontmatter({
+      milestoneId: "M001",
+      milestoneName: "Test",
+      projectName: "Proj",
+      generatedAt: "2026-04-15T10:00:00Z",
+      counts: { decisions: 0, lessons: 0, patterns: 0, surprises: 0 },
+      missingArtifacts: ["M001-VERIFICATION.md", "M001-UAT.md"],
+    });
+
+    assert.ok(result.includes("M001-VERIFICATION.md"));
+    assert.ok(result.includes("M001-UAT.md"));
+  });
+});
+
+// ─── extractProjectName ───────────────────────────────────────────────────────
+
+describe("extractProjectName", () => {
+  let tmpBase: string;
+
+  beforeEach(() => {
+    tmpBase = join(tmpdir(), `gsd-projname-test-${randomUUID()}`);
+    mkdirSync(join(tmpBase, ".gsd"), { recursive: true });
+  });
+
+  afterEach(() => {
+    rmSync(tmpBase, { recursive: true, force: true });
+  });
+
+  it("reads name from PROJECT.md frontmatter", () => {
+    writeFileSync(
+      join(tmpBase, ".gsd", "PROJECT.md"),
+      "---\nname: My Cool Project\nversion: 1\n---\n# Project\n",
+      "utf-8",
+    );
+
+    const result = extractProjectName(tmpBase);
+    assert.equal(result, "My Cool Project");
+  });
+
+  it("falls back to directory name when PROJECT.md absent", () => {
+    const result = extractProjectName(tmpBase);
+    // Should return the last path segment of tmpBase
+    assert.equal(result, tmpBase.split("/").at(-1));
+  });
+
+  it("falls back to directory name when PROJECT.md has no name field", () => {
+    writeFileSync(
+      join(tmpBase, ".gsd", "PROJECT.md"),
+      "---\nversion: 1\n---\n# Project\n",
+      "utf-8",
+    );
+
+    const result = extractProjectName(tmpBase);
+    assert.equal(result, tmpBase.split("/").at(-1));
+  });
+});