diff --git a/src/resources/extensions/gsd/tests/milestone-status-authoritative.test.ts b/src/resources/extensions/gsd/tests/milestone-status-authoritative.test.ts
new file mode 100644
index 000000000..94fdcf3c0
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/milestone-status-authoritative.test.ts
@@ -0,0 +1,116 @@
+/**
+ * Bug #2807: Web roadmap derives milestone status from slice heuristics
+ * instead of authoritative GSD milestone state.
+ *
+ * getMilestoneStatus() should prefer the authoritative `status` field on
+ * WorkspaceMilestoneTarget (populated from the engine registry) rather
+ * than inferring status from slice completion flags.
+ */
+import test from "node:test";
+import assert from "node:assert/strict";
+import { getMilestoneStatus } from "../../../../../web/lib/workspace-status.ts";
+
+// Inline type to avoid importing .tsx (not compiled to .js by test pipeline)
+interface TestMilestone {
+  id: string;
+  title: string;
+  roadmapPath?: string;
+  status?: "complete" | "active" | "pending" | "parked";
+  validationVerdict?: "pass" | "needs-attention" | "needs-remediation";
+  slices: Array<{ id: string; title: string; done: boolean; tasks: Array<{ id: string; title: string; done: boolean }> }>;
+}
+
+// ── Helpers ────────────────────────────────────────────────────────────────
+
+function makeMilestone(overrides: Partial<TestMilestone> & { id: string }): TestMilestone {
+  return {
+    title: overrides.id,
+    roadmapPath: undefined,
+    slices: [],
+    ...overrides,
+  };
+}
+
+// ── Tests ──────────────────────────────────────────────────────────────────
+
+test("getMilestoneStatus returns authoritative 'complete' even when slices are not all done", () => {
+  const milestone = makeMilestone({
+    id: "M001",
+    status: "complete",
+    slices: [
+      { id: "S01", title: "Slice 1", done: true, tasks: [] },
+      { id: "S02", title: "Slice 2", done: false, tasks: [] }, // not done
+    ],
+  });
+  // Before the fix, this would return "in-progress" because not all slices are done.
+  // After the fix, it should return "done" because authoritative status is "complete".
+  assert.equal(getMilestoneStatus(milestone, {}), "done");
+});
+
+test("getMilestoneStatus returns authoritative 'active' regardless of slice state", () => {
+  const milestone = makeMilestone({
+    id: "M002",
+    status: "active",
+    slices: [
+      { id: "S01", title: "Slice 1", done: true, tasks: [] },
+      { id: "S02", title: "Slice 2", done: true, tasks: [] },
+    ],
+  });
+  // Before the fix, this would return "done" because all slices are done.
+  // After the fix, it should return "in-progress" because authoritative status is "active".
+  assert.equal(getMilestoneStatus(milestone, {}), "in-progress");
+});
+
+test("getMilestoneStatus returns 'pending' for authoritative 'pending' even when some slices done", () => {
+  const milestone = makeMilestone({
+    id: "M003",
+    status: "pending",
+    slices: [
+      { id: "S01", title: "Slice 1", done: true, tasks: [] },
+      { id: "S02", title: "Slice 2", done: false, tasks: [] },
+    ],
+  });
+  // Before the fix, this would return "in-progress" because some slices are done.
+  // After the fix, it should return "pending".
+  assert.equal(getMilestoneStatus(milestone, {}), "pending");
+});
+
+test("getMilestoneStatus maps 'parked' to 'pending' item status", () => {
+  const milestone = makeMilestone({
+    id: "M004",
+    status: "parked",
+    slices: [
+      { id: "S01", title: "Slice 1", done: true, tasks: [] },
+    ],
+  });
+  // Parked milestones should render as pending in the UI
+  assert.equal(getMilestoneStatus(milestone, {}), "pending");
+});
+
+test("getMilestoneStatus falls back to heuristic when no authoritative status", () => {
+  // Backward compatibility: milestones without the status field should
+  // still work using the old slice-based heuristic.
+  const milestone = makeMilestone({
+    id: "M005",
+    slices: [
+      { id: "S01", title: "Slice 1", done: true, tasks: [] },
+      { id: "S02", title: "Slice 2", done: true, tasks: [] },
+    ],
+  });
+  assert.equal(getMilestoneStatus(milestone, {}), "done");
+});
+
+test("getMilestoneStatus exposes validationVerdict on milestone target", () => {
+  const milestone = makeMilestone({
+    id: "M006",
+    status: "complete",
+    validationVerdict: "needs-attention",
+    slices: [
+      { id: "S01", title: "Slice 1", done: true, tasks: [] },
+    ],
+  });
+  // The milestone should have the validationVerdict field available
+  assert.equal(milestone.validationVerdict, "needs-attention");
+  // And status should still be "done"
+  assert.equal(getMilestoneStatus(milestone, {}), "done");
+});
diff --git a/src/resources/extensions/gsd/workspace-index.ts b/src/resources/extensions/gsd/workspace-index.ts
index 8b270662b..28fa95df1 100644
--- a/src/resources/extensions/gsd/workspace-index.ts
+++ b/src/resources/extensions/gsd/workspace-index.ts
@@ -11,6 +11,7 @@ import {
   resolveTasksDir,
 } from "./paths.js";
 import { deriveState } from "./state.js";
+import { extractVerdict } from "./verdict-parser.js";
 import { milestoneIdSort, findMilestoneIds } from "./guided-flow.js";
 import type { RiskLevel } from "./types.js";
 import { getSliceBranchName, detectWorktreeName } from "./worktree.js";
@@ -42,6 +43,10 @@ export interface WorkspaceMilestoneTarget {
   id: string;
   title: string;
   roadmapPath?: string;
+  /** Authoritative milestone lifecycle status from the GSD state registry. */
+  status?: "complete" | "active" | "pending" | "parked";
+  /** Milestone validation verdict, when validation has been performed. */
+  validationVerdict?: "pass" | "needs-attention" | "needs-remediation";
   slices: WorkspaceSliceTarget[];
 }
 
@@ -192,6 +197,31 @@ export async function indexWorkspace(basePath: string, opts: IndexWorkspaceOptio
     phase: state.phase,
   };
 
+  // Enrich milestones with authoritative status from state registry (#2807)
+  if (state.registry) {
+    const registryMap = new Map(state.registry.map(e => [e.id, e]));
+    for (const milestone of milestones) {
+      const entry = registryMap.get(milestone.id);
+      if (entry) {
+        milestone.status = entry.status;
+      }
+    }
+  }
+
+  // Populate validationVerdict from VALIDATION files (#2807)
+  for (const milestone of milestones) {
+    const validationPath = resolveMilestoneFile(basePath, milestone.id, "VALIDATION");
+    if (validationPath) {
+      const validationContent = await loadFile(validationPath);
+      if (validationContent) {
+        const verdict = extractVerdict(validationContent);
+        if (verdict === "pass" || verdict === "needs-attention" || verdict === "needs-remediation") {
+          milestone.validationVerdict = verdict;
+        }
+      }
+    }
+  }
+
   const scopes: WorkspaceScopeTarget[] = [{ scope: "project", label: "project", kind: "project" }];
   for (const milestone of milestones) {
     scopes.push({ scope: milestone.id, label: `${milestone.id}: ${milestone.title}`, kind: "milestone" });
diff --git a/web/lib/gsd-workspace-store.tsx b/web/lib/gsd-workspace-store.tsx
index 123b914f8..7c0d1d399 100644
--- a/web/lib/gsd-workspace-store.tsx
+++ b/web/lib/gsd-workspace-store.tsx
@@ -125,37 +125,7 @@ export interface BridgeRuntimeSnapshot {
   lastError: BridgeLastError | null
 }
 
-export interface WorkspaceTaskTarget {
-  id: string
-  title: string
-  done: boolean
-  planPath?: string
-  summaryPath?: string
-}
-
-export type RiskLevel = "low" | "medium" | "high"
-
-export interface WorkspaceSliceTarget {
-  id: string
-  title: string
-  done: boolean
-  planPath?: string
-  summaryPath?: string
-  uatPath?: string
-  tasksDir?: string
-  branch?: string
-  risk?: RiskLevel
-  depends?: string[]
-  demo?: string
-  tasks: WorkspaceTaskTarget[]
-}
-
-export interface WorkspaceMilestoneTarget {
-  id: string
-  title: string
-  roadmapPath?: string
-  slices: WorkspaceSliceTarget[]
-}
+export type { WorkspaceTaskTarget, RiskLevel, WorkspaceSliceTarget, WorkspaceMilestoneTarget } from "./workspace-types.js"
 
 export interface WorkspaceScopeTarget {
   scope: string
diff --git a/web/lib/workspace-status.ts b/web/lib/workspace-status.ts
index 7fffa498c..7578b0042 100644
--- a/web/lib/workspace-status.ts
+++ b/web/lib/workspace-status.ts
@@ -2,7 +2,7 @@ import type {
   WorkspaceMilestoneTarget,
   WorkspaceSliceTarget,
   WorkspaceTaskTarget,
-} from "./gsd-workspace-store"
+} from "./workspace-types.js"
 
 export type ItemStatus = "done" | "in-progress" | "pending"
 
@@ -10,13 +10,27 @@ export function getMilestoneStatus(
   milestone: WorkspaceMilestoneTarget,
   active: { milestoneId?: string },
 ): ItemStatus {
-  if (milestone.slices.length > 0 && milestone.slices.every((slice) => slice.done)) {
+  // Prefer authoritative milestone status from GSD state registry (#2807)
+  if (milestone.status) {
+    switch (milestone.status) {
+      case "complete":
+        return "done"
+      case "active":
+        return "in-progress"
+      case "pending":
+      case "parked":
+        return "pending"
+    }
+  }
+
+  // Fallback: infer from slice completion (legacy / no status field)
+  if (milestone.slices.length > 0 && milestone.slices.every((slice: WorkspaceSliceTarget) => slice.done)) {
     return "done"
   }
   if (active.milestoneId === milestone.id) {
     return "in-progress"
   }
-  return milestone.slices.some((slice) => slice.done) ? "in-progress" : "pending"
+  return milestone.slices.some((slice: WorkspaceSliceTarget) => slice.done) ? "in-progress" : "pending"
 }
 
 export function getSliceStatus(
diff --git a/web/lib/workspace-types.ts b/web/lib/workspace-types.ts
new file mode 100644
index 000000000..5cfa99450
--- /dev/null
+++ b/web/lib/workspace-types.ts
@@ -0,0 +1,35 @@
+export interface WorkspaceTaskTarget {
+  id: string
+  title: string
+  done: boolean
+  planPath?: string
+  summaryPath?: string
+}
+
+export type RiskLevel = "low" | "medium" | "high"
+
+export interface WorkspaceSliceTarget {
+  id: string
+  title: string
+  done: boolean
+  planPath?: string
+  summaryPath?: string
+  uatPath?: string
+  tasksDir?: string
+  branch?: string
+  risk?: RiskLevel
+  depends?: string[]
+  demo?: string
+  tasks: WorkspaceTaskTarget[]
+}
+
+export interface WorkspaceMilestoneTarget {
+  id: string
+  title: string
+  roadmapPath?: string
+  /** Authoritative milestone lifecycle status from the GSD state registry. */
+  status?: "complete" | "active" | "pending" | "parked"
+  /** Milestone validation verdict, when validation has been performed. */
+  validationVerdict?: "pass" | "needs-attention" | "needs-remediation"
+  slices: WorkspaceSliceTarget[]
+}