diff --git a/src/server/sessions/sessionArchiveStore.test.ts b/src/server/sessions/sessionArchiveStore.test.ts
index d08186f..c11f579 100644
--- a/src/server/sessions/sessionArchiveStore.test.ts
+++ b/src/server/sessions/sessionArchiveStore.test.ts
@@ -1,6 +1,6 @@
 import { constants } from "node:fs";
 import { access, mkdtemp, mkdir, readFile, rm, writeFile } from "node:fs/promises";
-import { join } from "node:path";
+import { join, resolve } from "node:path";
 import { tmpdir } from "node:os";
 import { afterEach, describe, expect, it } from "vitest";
 import { SessionArchiveStore } from "./sessionArchiveStore.js";
@@ -118,6 +118,54 @@ describe("SessionArchiveStore", () => {
     }
     await expect(store.list()).resolves.toEqual([]);
   });
+
+  it("prefers exact persisted session IDs over prefix matches and canonicalizes stored cwd", async () => {
+    const root = await mkdtemp(join(tmpdir(), "pi-web-archive-prefix-"));
+    tempRoots.push(root);
+    const archiveFile = join(root, "archived-sessions.json");
+    const rawCwd = join(root, "workspace", "..", "workspace");
+    await writeFile(archiveFile, JSON.stringify({
+      sessions: [
+        {
+          sessionId: "abc123",
+          cwd: rawCwd,
+          archivedAt: "2026-01-01T00:00:00.000Z",
+          originalPath: "/sessions/abc123.jsonl",
+          archivePath: "/archive/abc123.jsonl",
+          messageCount: 3,
+          firstMessage: "prefix",
+          name: "Prefix match",
+          parentSessionPath: "/sessions/root.jsonl",
+        },
+        {
+          sessionId: "abc",
+          cwd: rawCwd,
+          archivedAt: "2026-01-01T00:00:00.000Z",
+          originalPath: "/sessions/abc.jsonl",
+          archivePath: "/archive/abc.jsonl",
+          messageCount: 1,
+          firstMessage: "exact",
+        },
+      ],
+    }), "utf8");
+
+    const store = new SessionArchiveStore(archiveFile, join(root, "archived-files"));
+
+    await expect(store.get("abc")).resolves.toMatchObject({
+      sessionId: "abc",
+      cwd: resolve(rawCwd),
+      firstMessage: "exact",
+    });
+    await expect(store.get("abc1")).resolves.toMatchObject({
+      sessionId: "abc123",
+      cwd: resolve(rawCwd),
+      firstMessage: "prefix",
+      name: "Prefix match",
+      parentSessionPath: "/sessions/root.jsonl",
+    });
+    await expect(store.isArchived("abc1")).resolves.toBe(true);
+    await expect(store.isArchived("missing")).resolves.toBe(false);
+  });
 });
 
 async function exists(path: string): Promise<boolean> {
diff --git a/src/server/sessions/sessionArchiveTree.test.ts b/src/server/sessions/sessionArchiveTree.test.ts
index f34db41..086445a 100644
--- a/src/server/sessions/sessionArchiveTree.test.ts
+++ b/src/server/sessions/sessionArchiveTree.test.ts
@@ -11,11 +11,11 @@ function candidate(id: string, options: Partial<SessionArchiveTreeCandidate> = {
 }
 
 describe("session archive tree planning", () => {
-  it("finds candidates by full id or prefix", () => {
-    const candidates = [candidate("abcdef"), candidate("xyz")];
+  it("finds candidates by exact id before falling back to a prefix", () => {
+    const candidates = [candidate("abcdef"), candidate("abc"), candidate("xyz")];
 
-    expect(findArchiveCandidateByIdOrPrefix(candidates, "abcdef")?.id).toBe("abcdef");
-    expect(findArchiveCandidateByIdOrPrefix(candidates, "abc")?.id).toBe("abcdef");
+    expect(findArchiveCandidateByIdOrPrefix(candidates, "abc")?.id).toBe("abc");
+    expect(findArchiveCandidateByIdOrPrefix(candidates, "abcd")?.id).toBe("abcdef");
     expect(findArchiveCandidateByIdOrPrefix(candidates, "missing")).toBeUndefined();
   });