diff --git a/src/resources/extensions/gsd/auto-artifact-paths.ts b/src/resources/extensions/gsd/auto-artifact-paths.ts
index 41b72fe6e..808f4819c 100644
--- a/src/resources/extensions/gsd/auto-artifact-paths.ts
+++ b/src/resources/extensions/gsd/auto-artifact-paths.ts
@@ -13,6 +13,7 @@ import {
   buildSliceFileName,
   buildTaskFileName,
 } from "./paths.js";
+import { parseUnitId } from "./unit-id.js";
 import { join } from "node:path";
 
 /**
@@ -23,9 +24,7 @@ export function resolveExpectedArtifactPath(
   unitId: string,
   base: string,
 ): string | null {
-  const parts = unitId.split("/");
-  const mid = parts[0]!;
-  const sid = parts[1];
+  const { milestone: mid, slice: sid, task: tid } = parseUnitId(unitId);
   switch (unitType) {
     case "discuss-milestone": {
       const dir = resolveMilestonePath(base, mid);
@@ -56,7 +55,6 @@ export function resolveExpectedArtifactPath(
       return dir ? join(dir, buildSliceFileName(sid!, "UAT")) : null;
     }
     case "execute-task": {
-      const tid = parts[2];
       const dir = resolveSlicePath(base, mid, sid!);
       return dir && tid
         ? join(dir, "tasks", buildTaskFileName(tid, "SUMMARY"))
@@ -93,38 +91,35 @@ export function diagnoseExpectedArtifact(
   unitId: string,
   base: string,
 ): string | null {
-  const parts = unitId.split("/");
-  const mid = parts[0];
-  const sid = parts[1];
+  const { milestone: mid, slice: sid, task: tid } = parseUnitId(unitId);
   switch (unitType) {
     case "discuss-milestone":
-      return `${relMilestoneFile(base, mid!, "CONTEXT")} (milestone context from discussion)`;
+      return `${relMilestoneFile(base, mid, "CONTEXT")} (milestone context from discussion)`;
     case "research-milestone":
-      return `${relMilestoneFile(base, mid!, "RESEARCH")} (milestone research)`;
+      return `${relMilestoneFile(base, mid, "RESEARCH")} (milestone research)`;
     case "plan-milestone":
-      return `${relMilestoneFile(base, mid!, "ROADMAP")} (milestone roadmap)`;
+      return `${relMilestoneFile(base, mid, "ROADMAP")} (milestone roadmap)`;
     case "research-slice":
-      return `${relSliceFile(base, mid!, sid!, "RESEARCH")} (slice research)`;
+      return `${relSliceFile(base, mid, sid!, "RESEARCH")} (slice research)`;
     case "plan-slice":
-      return `${relSliceFile(base, mid!, sid!, "PLAN")} (slice plan)`;
+      return `${relSliceFile(base, mid, sid!, "PLAN")} (slice plan)`;
     case "execute-task": {
-      const tid = parts[2];
-      return `Task ${tid} marked [x] in ${relSliceFile(base, mid!, sid!, "PLAN")} + summary written`;
+      return `Task ${tid} marked [x] in ${relSliceFile(base, mid, sid!, "PLAN")} + summary written`;
     }
     case "complete-slice":
-      return `Slice ${sid} marked [x] in ${relMilestoneFile(base, mid!, "ROADMAP")} + summary + UAT written`;
+      return `Slice ${sid} marked [x] in ${relMilestoneFile(base, mid, "ROADMAP")} + summary + UAT written`;
     case "replan-slice":
-      return `${relSliceFile(base, mid!, sid!, "REPLAN")} + updated ${relSliceFile(base, mid!, sid!, "PLAN")}`;
+      return `${relSliceFile(base, mid, sid!, "REPLAN")} + updated ${relSliceFile(base, mid, sid!, "PLAN")}`;
     case "rewrite-docs":
       return "Active overrides resolved in .gsd/OVERRIDES.md + plan documents updated";
     case "reassess-roadmap":
-      return `${relSliceFile(base, mid!, sid!, "ASSESSMENT")} (roadmap reassessment)`;
+      return `${relSliceFile(base, mid, sid!, "ASSESSMENT")} (roadmap reassessment)`;
     case "run-uat":
-      return `${relSliceFile(base, mid!, sid!, "UAT")} (UAT result)`;
+      return `${relSliceFile(base, mid, sid!, "UAT")} (UAT result)`;
     case "validate-milestone":
-      return `${relMilestoneFile(base, mid!, "VALIDATION")} (milestone validation report)`;
+      return `${relMilestoneFile(base, mid, "VALIDATION")} (milestone validation report)`;
     case "complete-milestone":
-      return `${relMilestoneFile(base, mid!, "SUMMARY")} (milestone summary)`;
+      return `${relMilestoneFile(base, mid, "SUMMARY")} (milestone summary)`;
     default:
       return null;
   }
diff --git a/src/resources/extensions/gsd/auto-dashboard.ts b/src/resources/extensions/gsd/auto-dashboard.ts
index e926f8253..79751b698 100644
--- a/src/resources/extensions/gsd/auto-dashboard.ts
+++ b/src/resources/extensions/gsd/auto-dashboard.ts
@@ -25,6 +25,7 @@ import { computeProgressScore } from "./progress-score.js";
 import { getActiveWorktreeName } from "./worktree-command.js";
 import { loadEffectiveGSDPreferences, getGlobalGSDPreferencesPath } from "./preferences.js";
 import { resolveServiceTierIcon, getEffectiveServiceTier } from "./service-tier.js";
+import { parseUnitId } from "./unit-id.js";
 
 // ─── UAT Slice Extraction ─────────────────────────────────────────────────────
 
@@ -33,8 +34,8 @@ import { resolveServiceTierIcon, getEffectiveServiceTier } from "./service-tier.
  * Returns null if the format doesn't match.
  */
 export function extractUatSliceId(unitId: string): string | null {
-  const parts = unitId.split("/");
-  if (parts.length >= 2 && parts[1]!.startsWith("S")) return parts[1]!;
+  const { slice } = parseUnitId(unitId);
+  if (slice?.startsWith("S")) return slice;
   return null;
 }
 
diff --git a/src/resources/extensions/gsd/auto-post-unit.ts b/src/resources/extensions/gsd/auto-post-unit.ts
index 1aa4471ad..0704deb8d 100644
--- a/src/resources/extensions/gsd/auto-post-unit.ts
+++ b/src/resources/extensions/gsd/auto-post-unit.ts
@@ -23,6 +23,7 @@ import {
   buildTaskFileName,
 } from "./paths.js";
 import { invalidateAllCaches } from "./cache.js";
+import { parseUnitId } from "./unit-id.js";
 import { closeoutUnit, type CloseoutOptions } from "./auto-unit-closeout.js";
 import {
   autoCommitCurrentBranch,
@@ -91,11 +92,10 @@ export function detectRogueFileWrites(
 ): RogueFileWrite[] {
   if (!isDbAvailable()) return [];
 
-  const parts = unitId.split("/");
+  const { milestone: mid, slice: sid, task: tid } = parseUnitId(unitId);
   const rogues: RogueFileWrite[] = [];
 
   if (unitType === "execute-task") {
-    const [mid, sid, tid] = parts;
     if (!mid || !sid || !tid) return [];
 
     const summaryPath = resolveTaskFile(basePath, mid, sid, tid, "SUMMARY");
@@ -106,7 +106,6 @@ export function detectRogueFileWrites(
       rogues.push({ path: summaryPath, unitType, unitId });
     }
   } else if (unitType === "complete-slice") {
-    const [mid, sid] = parts;
     if (!mid || !sid) return [];
 
     const summaryPath = resolveSliceFile(basePath, mid, sid, "SUMMARY");
@@ -117,7 +116,6 @@ export function detectRogueFileWrites(
       rogues.push({ path: summaryPath, unitType, unitId });
     }
   } else if (unitType === "plan-milestone") {
-    const [mid] = parts;
     if (!mid) return [];
 
     const roadmapPath = resolveMilestoneFile(basePath, mid, "ROADMAP");
@@ -135,7 +133,6 @@ export function detectRogueFileWrites(
       rogues.push({ path: roadmapPath, unitType, unitId });
     }
   } else if (unitType === "plan-slice" || unitType === "replan-slice") {
-    const [mid, sid] = parts;
     if (!mid || !sid) return [];
 
     const planPath = resolveSliceFile(basePath, mid, sid, "PLAN");
@@ -159,7 +156,6 @@ export function detectRogueFileWrites(
       rogues.push({ path: replanPath, unitType, unitId });
     }
   } else if (unitType === "reassess-roadmap") {
-    const [mid, sid] = parts;
     if (!mid || !sid) return [];
 
     const assessPath = resolveSliceFile(basePath, mid, sid, "ASSESSMENT");
@@ -176,7 +172,6 @@ export function detectRogueFileWrites(
       }
     }
   } else if (unitType === "plan-task") {
-    const [mid, sid, tid] = parts;
     if (!mid || !sid || !tid) return [];
 
     const taskPlanPath = resolveTaskFile(basePath, mid, sid, tid, "PLAN");
@@ -249,8 +244,7 @@ export async function postUnitPreVerification(pctx: PostUnitContext, opts?: PreV
       let taskContext: TaskCommitContext | undefined;
 
       if (s.currentUnit.type === "execute-task") {
-        const parts = s.currentUnit.id.split("/");
-        const [mid, sid, tid] = parts;
+        const { milestone: mid, slice: sid, task: tid } = parseUnitId(s.currentUnit.id);
         if (mid && sid && tid) {
           const summaryPath = resolveTaskFile(s.basePath, mid, sid, tid, "SUMMARY");
           if (summaryPath) {
@@ -354,8 +348,7 @@ export async function postUnitPreVerification(pctx: PostUnitContext, opts?: PreV
     // Reactive state cleanup on slice completion
     if (s.currentUnit.type === "complete-slice") {
       try {
-        const parts = s.currentUnit.id.split("/");
-        const [mid, sid] = parts;
+        const { milestone: mid, slice: sid } = parseUnitId(s.currentUnit.id);
         if (mid && sid) {
           const { clearReactiveState } = await import("./reactive-graph.js");
           clearReactiveState(s.basePath, mid, sid);
@@ -440,8 +433,7 @@ export async function postUnitPreVerification(pctx: PostUnitContext, opts?: PreV
       // from DB data before giving up (e.g. research-slice produces PLAN from engine).
       if (!triggerArtifactVerified) {
         try {
-          const parts = s.currentUnit.id.split("/");
-          const [mid, sid] = parts;
+          const { milestone: mid, slice: sid } = parseUnitId(s.currentUnit.id);
           if (mid && sid) {
             const regenerated = regenerateIfMissing(s.basePath, mid, sid, "PLAN");
             if (regenerated) {
@@ -541,8 +533,7 @@ export async function postUnitPostVerification(pctx: PostUnitContext): Promise<"
 
         // ── State reset: undo the completion so deriveState re-derives the unit ──
         try {
-          const parts = trigger.unitId.split("/");
-          const [mid, sid, tid] = parts;
+          const { milestone: mid, slice: sid, task: tid } = parseUnitId(trigger.unitId);
 
           // 1. Reset task status in DB and re-render plan checkboxes
           if (mid && sid && tid) {
diff --git a/src/resources/extensions/gsd/auto-start.ts b/src/resources/extensions/gsd/auto-start.ts
index e47dc5069..533edafba 100644
--- a/src/resources/extensions/gsd/auto-start.ts
+++ b/src/resources/extensions/gsd/auto-start.ts
@@ -66,6 +66,7 @@ import {
   isDebugEnabled,
   getDebugLogPath,
 } from "./debug-logger.js";
+import { parseUnitId } from "./unit-id.js";
 import type { AutoSession } from "./auto/session.js";
 import {
   existsSync,
@@ -200,7 +201,7 @@ export async function bootstrapAutoSession(
         );
         return releaseLockAndReturn();
       }
-      const recoveredMid = crashLock.unitId.split("/")[0];
+      const recoveredMid = parseUnitId(crashLock.unitId).milestone;
       const milestoneAlreadyComplete = recoveredMid
         ? !!resolveMilestoneFile(base, recoveredMid, "SUMMARY")
         : false;
diff --git a/src/resources/extensions/gsd/auto-verification.ts b/src/resources/extensions/gsd/auto-verification.ts
index 8a0c6ca55..e9b4a6790 100644
--- a/src/resources/extensions/gsd/auto-verification.ts
+++ b/src/resources/extensions/gsd/auto-verification.ts
@@ -12,6 +12,7 @@
 
 import type { ExtensionContext, ExtensionAPI } from "@gsd/pi-coding-agent";
 import { resolveSliceFile, resolveSlicePath } from "./paths.js";
+import { parseUnitId } from "./unit-id.js";
 import { isDbAvailable, getTask } from "./gsd-db.js";
 import { loadEffectiveGSDPreferences } from "./preferences.js";
 import {
@@ -60,10 +61,9 @@ export async function runPostUnitVerification(
     const prefs = effectivePrefs?.preferences;
 
     // Read task plan verify field
-    const parts = s.currentUnit.id.split("/");
+    const { milestone: mid, slice: sid, task: tid } = parseUnitId(s.currentUnit.id);
     let taskPlanVerify: string | undefined;
-    if (parts.length >= 3) {
-      const [mid, sid, tid] = parts;
+    if (mid && sid && tid) {
       if (isDbAvailable()) {
         taskPlanVerify = getTask(mid, sid, tid)?.verify;
       }
@@ -141,9 +141,8 @@ export async function runPostUnitVerification(
 
     // Write verification evidence JSON
     const attempt = s.verificationRetryCount.get(s.currentUnit.id) ?? 0;
-    if (parts.length >= 3) {
+    if (mid && sid && tid) {
       try {
-        const [mid, sid, tid] = parts;
         const sDir = resolveSlicePath(s.basePath, mid, sid);
         if (sDir) {
           const tasksDir = join(sDir, "tasks");