diff --git a/scripts/work-items.js b/scripts/work-items.js
index 8a130651c..c9161015c 100644
--- a/scripts/work-items.js
+++ b/scripts/work-items.js
@@ -176,8 +176,36 @@ function slugifyWorkItemSegment(value) {
   );
 }
 
+function normalizeGithubRepo(repo) {
+  return typeof repo === 'string' ? repo.toLowerCase() : '';
+}
+
 function githubWorkItemId(repo, type, number) {
-  return `github-${slugifyWorkItemSegment(repo)}-${type}-${number}`;
+  return `github-${encodeURIComponent(normalizeGithubRepo(repo))}-${type}-${number}`;
+}
+
+function isSameGithubWorkItem(existing, incoming) {
+  return existing
+    && existing.source === incoming.source
+    && existing.sourceId === incoming.sourceId
+    && existing.metadata?.syncedBy === 'ecc-work-items-sync-github'
+    && normalizeGithubRepo(existing.metadata.repo) === normalizeGithubRepo(incoming.metadata.repo);
+}
+
+function resolveGithubWorkItemId(store, item) {
+  const existing = store.getWorkItemById(item.id);
+  if (existing) {
+    if (!isSameGithubWorkItem(existing, item)) {
+      throw new Error(`GitHub work item ID collision: ${item.id} belongs to a different item.`);
+    }
+    return item.id;
+  }
+
+  // Keep references to older imports intact, but never reuse a slug belonging
+  // to another repository. Prefer an existing canonical ID on every sync.
+  const type = item.source === 'github-pr' ? 'pr' : 'issue';
+  const legacyId = `github-${slugifyWorkItemSegment(item.metadata.repo)}-${type}-${item.sourceId}`;
+  return isSameGithubWorkItem(store.getWorkItemById(legacyId), item) ? legacyId : item.id;
 }
 
 function githubPrStatus(pr) {
@@ -245,7 +273,7 @@ function closeStaleGithubItems(store, repo, activeIds, options = {}) {
     if (!item.metadata || item.metadata.syncedBy !== 'ecc-work-items-sync-github') {
       continue;
     }
-    if (item.metadata.repo !== repo || activeIds.has(item.id)) {
+    if (normalizeGithubRepo(item.metadata.repo) !== normalizeGithubRepo(repo) || activeIds.has(item.id)) {
       continue;
     }
     if (item.status === 'closed' || item.status === 'done') {
@@ -281,10 +309,12 @@ function syncGithubWorkItems(store, options) {
   const items = [];
   for (const pr of prs) {
     const payload = buildGithubPrWorkItem(repo, pr, options);
-    activeIds.add(payload.id);
+    const id = resolveGithubWorkItemId(store, payload);
+    activeIds.add(id);
     items.push(
       store.upsertWorkItem({
         ...payload,
+        id,
         createdAt: undefined,
         updatedAt: syncedAt
       })
@@ -292,10 +322,12 @@ function syncGithubWorkItems(store, options) {
   }
   for (const issue of issues) {
     const payload = buildGithubIssueWorkItem(repo, issue, options);
-    activeIds.add(payload.id);
+    const id = resolveGithubWorkItemId(store, payload);
+    activeIds.add(id);
     items.push(
       store.upsertWorkItem({
         ...payload,
+        id,
         createdAt: undefined,
         updatedAt: syncedAt
       })
diff --git a/tests/lib/state-store.test.js b/tests/lib/state-store.test.js
index a1e2f045c..800a32e35 100644
--- a/tests/lib/state-store.test.js
+++ b/tests/lib/state-store.test.js
@@ -980,7 +980,7 @@ async function runTests() {
       assert.strictEqual(syncPayload.issueCount, 1);
       assert.strictEqual(syncPayload.closedCount, 0);
       assert.strictEqual(syncPayload.items.length, 3);
-      assert.strictEqual(syncPayload.items[0].id, 'github-affaan-m-ecc-pr-3');
+      assert.strictEqual(syncPayload.items[0].id, 'github-affaan-m%2Fecc-pr-3');
       assert.strictEqual(syncPayload.items[0].status, 'blocked');
       assert.strictEqual(syncPayload.items[1].status, 'needs-review');
       assert.strictEqual(syncPayload.items[2].metadata.labels[0], 'release');
diff --git a/tests/scripts/work-items-identity.test.js b/tests/scripts/work-items-identity.test.js
new file mode 100644
index 000000000..581251103
--- /dev/null
+++ b/tests/scripts/work-items-identity.test.js
@@ -0,0 +1,265 @@
+'use strict';
+
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const os = require('node:os');
+const path = require('node:path');
+const { spawnSync } = require('node:child_process');
+const { test } = require('node:test');
+const { createStateStore } = require('../../scripts/lib/state-store');
+
+const CLI = path.join(__dirname, '..', '..', 'scripts', 'work-items.js');
+const SYNC_MARKER = 'ecc-work-items-sync-github';
+
+function fixture(t) {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'ecc-work-item-identity-'));
+  const dbPath = path.join(dir, 'state.db');
+  const responsePath = path.join(dir, 'response.json');
+  const shimPath = path.join(dir, 'gh-shim.cjs');
+  fs.writeFileSync(shimPath, [
+    "const fs = require('node:fs');",
+    'const response = JSON.parse(fs.readFileSync(process.env.ECC_IDENTITY_RESPONSE, "utf8"));',
+    'process.stdout.write(JSON.stringify(response[process.argv[2]]));'
+  ].join('\n'));
+  t.after(() => fs.rmSync(dir, { recursive: true, force: true }));
+
+  function run(args) {
+    return spawnSync(process.execPath, [CLI, ...args, '--db', dbPath], {
+      encoding: 'utf8',
+      env: { ...process.env, ECC_GH_SHIM: shimPath, ECC_IDENTITY_RESPONSE: responsePath }
+    });
+  }
+
+  function sync(repo, response = { issue: [], pr: [] }, args = []) {
+    fs.writeFileSync(responsePath, JSON.stringify(response));
+    return run(['sync-github', '--repo', repo, '--json', ...args]);
+  }
+
+  function syncItems(repo, response, args) {
+    const result = sync(repo, response, args);
+    assert.equal(result.status, 0, result.stderr);
+    return JSON.parse(result.stdout);
+  }
+
+  async function withStore(fn) {
+    const store = await createStateStore({ dbPath });
+    try {
+      return fn(store);
+    } finally {
+      store.close();
+    }
+  }
+
+  return { run, sync, syncItems, withStore };
+}
+
+function responseFor(repo, types = ['issue', 'pr']) {
+  const entry = type => ({
+    number: 1,
+    title: `${repo} ${type}`,
+    url: `https://github.com/${repo}/${type === 'pr' ? 'pull' : 'issues'}/1`,
+    author: { login: 'author' },
+    labels: [],
+    isDraft: false,
+    mergeStateStatus: 'CLEAN'
+  });
+  return {
+    issue: types.includes('issue') ? [entry('issue')] : [],
+    pr: types.includes('pr') ? [entry('pr')] : []
+  };
+}
+
+function legacyItem(repo, type, overrides = {}) {
+  return {
+    id: `github-${repo.toLowerCase().replace(/[^a-z0-9]+/g, '-').replace(/^-+|-+$/g, '')}-${type}-1`,
+    source: `github-${type}`,
+    sourceId: '1',
+    title: 'Previously imported item',
+    status: 'needs-review',
+    createdAt: '2020-01-02T03:04:05.000Z',
+    metadata: { repo, type: type === 'pr' ? 'pull_request' : 'issue', syncedBy: SYNC_MARKER },
+    ...overrides
+  };
+}
+
+test('sync keeps punctuation and owner/repository boundaries distinct for issues and PRs', async t => {
+  const f = fixture(t);
+  const repos = ['acme/tool-kit', 'acme/tool_kit', 'acme/tool.kit', 'acme-tool/kit'];
+  const ids = [];
+  for (const repo of repos) {
+    const first = f.syncItems(repo, responseFor(repo));
+    const repeated = f.syncItems(repo, responseFor(repo));
+    assert.deepEqual(repeated.items.map(item => item.id), first.items.map(item => item.id));
+    ids.push(...first.items.map(item => item.id));
+  }
+  assert.equal(new Set(ids).size, repos.length * 2, 'every repository/type identity must have its own ID');
+  const rows = await f.withStore(store => store.listWorkItems({ limit: 100 }).items);
+  assert.equal(rows.length, repos.length * 2);
+  for (const repo of repos) {
+    for (const type of ['issue', 'pr']) {
+      const row = rows.find(item => item.metadata.repo === repo && item.source === `github-${type}`);
+      assert.ok(row, `${repo} ${type} remains stored`);
+      assert.equal(row.status, 'needs-review');
+      assert.equal(row.url, responseFor(repo)[type][0].url);
+    }
+  }
+});
+
+for (const type of ['issue', 'pr']) {
+  test(`${type}: reuse a matching legacy ID and preserve creation time and explicit linkage`, async t => {
+    const f = fixture(t);
+    const repo = 'Acme/Tool_Kit';
+    const legacy = legacyItem(repo, type, { sessionId: 'session-42', repoRoot: '/workspace/tool-kit' });
+    await f.withStore(store => {
+      store.upsertSession({ id: 'session-42', adapterId: 'manual', harness: 'codex', state: 'running' });
+      store.upsertWorkItem(legacy);
+    });
+    const args = ['--session', 'session-42', '--repo-root', '/workspace/tool-kit'];
+    const synced = f.syncItems(repo.toLowerCase(), responseFor(repo, [type]), args);
+    assert.equal(synced.items[0].id, legacy.id);
+    assert.equal(synced.items[0].createdAt, legacy.createdAt);
+    assert.equal(synced.items[0].sessionId, legacy.sessionId);
+    assert.equal(synced.items[0].repoRoot, legacy.repoRoot);
+    assert.equal(synced.items[0].title, `${type === 'pr' ? 'PR' : 'Issue'} #1: ${repo} ${type}`);
+    const repeated = f.syncItems(repo, responseFor(repo, [type]), args);
+    assert.equal(repeated.items[0].id, legacy.id);
+    assert.equal(repeated.closedCount, 0);
+    assert.equal(await f.withStore(store => store.listWorkItems({ limit: 100 }).items.length), 1);
+  });
+
+  test(`${type}: a colliding legacy repository is not overwritten`, async t => {
+    const f = fixture(t);
+    const original = await f.withStore(store => store.upsertWorkItem(legacyItem('acme/tool-kit', type)));
+    const incoming = f.syncItems('acme/tool_kit', responseFor('acme/tool_kit', [type])).items[0];
+    assert.notEqual(incoming.id, original.id);
+    assert.deepEqual(await f.withStore(store => store.getWorkItemById(original.id)), original);
+    assert.equal(await f.withStore(store => store.listWorkItems({ limit: 100 }).items.length), 2);
+  });
+}
+
+test('legacy reuse requires the matching source, number, sync marker, and repository', async t => {
+  const variants = [
+    { source: 'manual' },
+    { sourceId: '2' },
+    { metadata: { repo: 'acme/tool-kit', type: 'issue' } },
+    ...[null, 42, { toString: 5 }].map(repo => ({
+      metadata: { repo, type: 'issue', syncedBy: SYNC_MARKER }
+    }))
+  ];
+  for (const overrides of variants) {
+    await t.test(JSON.stringify(overrides), async subtest => {
+      const f = fixture(subtest);
+      const original = await f.withStore(store => store.upsertWorkItem(legacyItem('acme/tool-kit', 'issue', {
+        ...overrides,
+        status: 'done'
+      })));
+      const incoming = f.syncItems('acme/tool-kit', responseFor('acme/tool-kit', ['issue'])).items[0];
+      assert.notEqual(incoming.id, original.id);
+      assert.deepEqual(await f.withStore(store => store.getWorkItemById(original.id)), original);
+    });
+  }
+});
+
+test('canonical IDs stay stable across casing changes and when the legacy ID is vacant', async t => {
+  const f = fixture(t);
+  const repo = 'Acme/Tool_Kit';
+  const canonical = legacyItem(repo, 'issue', {
+    id: `github-${encodeURIComponent(repo.toLowerCase())}-issue-1`
+  });
+  await f.withStore(store => store.upsertWorkItem(canonical));
+  for (const spelling of [repo.toLowerCase(), repo.toUpperCase()]) {
+    const result = f.syncItems(spelling, responseFor(spelling, ['issue']));
+    assert.equal(result.items[0].id, canonical.id);
+    assert.equal(result.closedCount, 0);
+    assert.equal(result.items[0].createdAt, canonical.createdAt);
+  }
+  assert.equal(await f.withStore(store => store.listWorkItems({ limit: 100 }).items.length), 1);
+});
+
+test('canonical IDs take precedence when a matching legacy record also exists', async t => {
+  const f = fixture(t);
+  const repo = 'acme/tool-kit';
+  const legacy = await f.withStore(store => store.upsertWorkItem(legacyItem(repo, 'issue', { status: 'done' })));
+  const canonical = legacyItem(repo, 'issue', {
+    id: `github-${encodeURIComponent(repo)}-issue-1`,
+    createdAt: '2021-02-03T04:05:06.000Z'
+  });
+  await f.withStore(store => store.upsertWorkItem(canonical));
+  const result = f.syncItems(repo, responseFor(repo, ['issue']));
+  assert.equal(result.items[0].id, canonical.id);
+  assert.equal(result.items[0].createdAt, canonical.createdAt);
+  assert.equal(result.items[0].status, 'needs-review');
+  assert.deepEqual(await f.withStore(store => store.getWorkItemById(legacy.id)), legacy);
+  assert.equal(await f.withStore(store => store.listWorkItems({ limit: 100 }).items.length), 2);
+});
+
+test('a canonical ID occupied by a different identity fails without overwriting it', async t => {
+  const f = fixture(t);
+  const repo = 'acme/tool-kit';
+  const original = await f.withStore(store => store.upsertWorkItem({
+    id: `github-${encodeURIComponent(repo)}-issue-1`,
+    source: 'manual',
+    title: 'Unrelated local work',
+    status: 'open'
+  }));
+  const result = f.sync(repo, responseFor(repo, ['issue']));
+  assert.notEqual(result.status, 0);
+  assert.match(result.stderr, /collision|already|different|conflict/i);
+  assert.deepEqual(await f.withStore(store => store.getWorkItemById(original.id)), original);
+  assert.equal(await f.withStore(store => store.listWorkItems({ limit: 100 }).items.length), 1);
+});
+
+test('closing stale items isolates punctuation variants and recognizes repository casing', async t => {
+  const f = fixture(t);
+  const legacy = legacyItem('Acme/Tool-Kit', 'issue');
+  await f.withStore(store => store.upsertWorkItem(legacy));
+  const own = f.syncItems('Acme/Tool-Kit', responseFor('Acme/Tool-Kit')).items;
+  const neighbor = f.syncItems('acme/tool_kit', responseFor('acme/tool_kit')).items;
+  const closed = f.syncItems('ACME/TOOL-KIT', { issue: [], pr: [] });
+  assert.deepEqual(closed.closedItems.map(item => item.id).sort(), own.map(item => item.id).sort());
+  assert.equal(closed.closedCount, 2);
+  for (const item of own) {
+    assert.equal((await f.withStore(store => store.getWorkItemById(item.id))).status, 'closed');
+  }
+  for (const item of neighbor) {
+    assert.equal((await f.withStore(store => store.getWorkItemById(item.id))).status, 'needs-review');
+  }
+  assert.equal(f.syncItems('acme/tool-kit', { issue: [], pr: [] }).closedCount, 0);
+});
+
+test('encoded IDs round-trip through display, claim, and close commands', async t => {
+  const f = fixture(t);
+  const repo = 'acme/tool_kit';
+  const response = responseFor(repo, ['issue']);
+  const imported = f.syncItems(repo, {
+    ...response,
+    issue: response.issue.map(issue => ({ ...issue, author: null }))
+  }).items[0];
+  assert.match(imported.id, /%2F/);
+
+  for (const args of [
+    ['sync-github', '--repo', repo],
+    ['show', imported.id],
+    ['list'],
+    ['claim', imported.id, '--owner', 'maintainer', '--as', 'human'],
+    ['close', imported.id]
+  ]) {
+    const result = f.run(args);
+    assert.equal(result.status, 0, result.stderr);
+    assert.ok(result.stdout.includes(imported.id), `${args[0]} displays the exact ID`);
+  }
+
+  const shown = f.run(['show', imported.id, '--json']);
+  assert.equal(shown.status, 0, shown.stderr);
+  const item = JSON.parse(shown.stdout);
+  assert.equal(item.id, imported.id);
+  assert.equal(item.status, 'done');
+  assert.equal(item.owner, 'maintainer');
+  assert.equal(item.metadata.assigneeKind, 'human');
+  assert.equal(item.metadata.repo, repo);
+  assert.equal(item.source, imported.source);
+  assert.equal(item.sourceId, imported.sourceId);
+  assert.equal(item.createdAt, imported.createdAt);
+  assert.equal(item.url, imported.url);
+  assert.deepEqual(await f.withStore(store => store.listWorkItems({ limit: 100 }).items), [item]);
+});