Merge pull request 'feat: add lease and collision visibility to web UI (Closes #433)' (#454) from feat/issue-433-lease-visibility into master

docs/webui-local-dev.md

@@ -46,7 +46,8 @@ Optional environment variables:
 | `/runtime` | Stub — MCP runtime health (#430) |
 | `/audit` | Stub — report audit paste (#431) |
 | `/worktrees` | Stub — hygiene dashboard (#432) |
-| `/leases` | Stub — lease visibility (#433) |
+| `/leases` | Lease and collision visibility (#433) |
+| `/api/leases` | JSON lease/collision export |
 
 All routes are GET-only. POST/PUT/PATCH/DELETE return `405` with
 `read-only-mvp`.
@@ -82,8 +83,16 @@ credentials. The UI surfaces pagination proof (returned count, pages fetched,
 If credentials are missing or the fetch fails, the page shows an explicit error
 instead of an empty queue (fail closed).
 
+## Lease visibility (#433)
+
+`/leases` surfaces read-only lease and collision state: local issue lock file,
+in-progress claim inventory (#268), reviewer PR lease comments when present
+(`<!-- mcp-review-lease:v1 -->`, #407), duplicate open PRs per issue (#400),
+and duplicate local branches per issue. Links to collision-history backend
+issues (#267, #268, #400, #407) are included. No lease acquire/release from UI.
+
 ## Tests
 
 ```bash
-pytest tests/test_webui_skeleton.py tests/test_webui_project_registry.py tests/test_webui_prompt_library.py tests/test_webui_queue_dashboard.py -q
+pytest tests/test_webui_skeleton.py tests/test_webui_project_registry.py tests/test_webui_prompt_library.py tests/test_webui_queue_dashboard.py tests/test_webui_lease_visibility.py -q
 ```

tests/test_webui_lease_visibility.py

@@ -0,0 +1,94 @@
+"""Tests for web UI lease visibility (#433)."""
+import sys
+import unittest
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
+
+from starlette.testclient import TestClient
+
+from webui.app import create_app
+from webui.lease_loader import (
+    _duplicate_branch_warnings,
+    _duplicate_pr_warnings,
+    load_lease_snapshot,
+    parse_reviewer_lease_comment,
+    snapshot_to_dict,
+)
+
+
+class TestLeaseLoader(unittest.TestCase):
+    def test_parse_reviewer_lease_comment(self):
+        body = (
+            "<!-- mcp-review-lease:v1 -->\n"
+            "pr: #42\n"
+            "reviewer_identity: sysadmin\n"
+            "profile: prgs-reviewer\n"
+            "phase: validating\n"
+            "expires_at: 2026-07-07T20:00:00Z\n"
+        )
+        parsed = parse_reviewer_lease_comment(body)
+        self.assertIsNotNone(parsed)
+        assert parsed is not None
+        self.assertEqual(parsed["pr_number"], 42)
+        self.assertEqual(parsed["phase"], "validating")
+
+    def test_duplicate_pr_warnings(self):
+        raw_prs = [
+            {"number": 1, "title": "Closes #99", "body": ""},
+            {"number": 2, "title": "fixes #99", "body": ""},
+        ]
+        warnings = _duplicate_pr_warnings(raw_prs)
+        self.assertEqual(len(warnings), 1)
+        self.assertEqual(warnings[0].issue_number, 99)
+        self.assertEqual(warnings[0].pr_numbers, (1, 2))
+
+    def test_duplicate_branch_warnings(self):
+        warnings = _duplicate_branch_warnings([
+            "feat/issue-12-a",
+            "feat/issue-12-b",
+            "master",
+        ])
+        self.assertEqual(len(warnings), 1)
+        self.assertEqual(warnings[0].issue_number, 12)
+
+    def test_load_snapshot_with_injected_fetch(self):
+        def fetch_prs(_h, _o, _r, _a):
+            return ([], None)
+
+        def fetch_issues(_h, _o, _r, _a):
+            return ([], None)
+
+        snapshot = load_lease_snapshot(
+            fetch_prs=fetch_prs,
+            fetch_issues=fetch_issues,
+            fetch_comments=lambda *_a, **_k: [],
+            issue_lock_path=str(Path("/nonexistent/lock.json")),
+        )
+        data = snapshot_to_dict(snapshot)
+        self.assertIn("claim_inventory", data)
+        self.assertIn("collision_history", data)
+
+
+class TestLeaseRoutes(unittest.TestCase):
+    def setUp(self):
+        self.client = TestClient(create_app())
+
+    def test_leases_page_renders(self):
+        response = self.client.get("/leases")
+        self.assertEqual(response.status_code, 200)
+        self.assertIn("Leases", response.text)
+        self.assertIn("Collision warnings", response.text)
+        self.assertNotIn("child issue", response.text.lower())
+
+    def test_api_leases_json(self):
+        response = self.client.get("/api/leases")
+        self.assertEqual(response.status_code, 200)
+        data = response.json()
+        self.assertIn("claim_inventory", data)
+        self.assertIn("duplicate_prs", data)
+        self.assertIn("reviewer_leases", data)
+
+
+if __name__ == "__main__":
+    unittest.main()

tests/test_webui_skeleton.py

@@ -46,10 +46,14 @@ class TestWebuiSkeleton(unittest.TestCase):
         self.assertEqual(response.status_code, 200)
         self.assertIn("Gitea-Tools", response.text)
 
+    def test_leases_is_implemented(self):
+        response = self.client.get("/leases")
+        self.assertEqual(response.status_code, 200)
+        self.assertIn("Leases", response.text)
+        self.assertIn("Collision warnings", response.text)
+
     def test_extra_stub_routes(self):
-        for path in ("/worktrees", "/leases"):
-            with self.subTest(path=path):
-                self.assertEqual(self.client.get(path).status_code, 200)
+        self.assertEqual(self.client.get("/worktrees").status_code, 200)
 
     def test_post_is_rejected(self):
         response = self.client.post("/health")
@@ -62,10 +66,10 @@ class TestWebuiSkeleton(unittest.TestCase):
         self.assertIn("Live queue", response.text)
 
     def test_nav_links_on_all_pages(self):
-        for path in ("/", "/queue", "/projects", "/prompts", "/runtime", "/audit"):
+        for path in ("/", "/queue", "/projects", "/prompts", "/runtime", "/audit", "/leases"):
             with self.subTest(path=path):
                 text = self.client.get(path).text
-                for href in ("/queue", "/projects", "/prompts", "/runtime", "/audit"):
+                for href in ("/queue", "/projects", "/prompts", "/runtime", "/audit", "/leases"):
                     self.assertIn(f'href="{href}"', text)
 
 

webui/app.py

@@ -14,6 +14,8 @@ from webui.project_registry import find_project, load_registry, registry_to_dict
 from webui.project_views import render_project_detail, render_projects_list
 from webui.prompt_library import find_prompt, library_to_dict
 from webui.prompt_views import render_prompt_detail, render_prompts_page
+from webui.lease_loader import load_lease_snapshot, snapshot_to_dict as lease_snapshot_to_dict
+from webui.lease_views import render_leases_page
 from webui.queue_loader import load_queue_snapshot, snapshot_to_dict
 from webui.queue_views import render_queue_page
 
@@ -141,10 +143,12 @@ async def worktrees(_request: Request) -> HTMLResponse:
 
 
 async def leases(_request: Request) -> HTMLResponse:
-    return _stub_page(
-        "Leases",
-        "Lease visibility will show active issue and reviewer PR leases.",
-    )
+    snapshot = load_lease_snapshot()
+    return HTMLResponse(render_leases_page(snapshot))
+
+
+async def api_leases(_request: Request) -> JSONResponse:
+    return JSONResponse(lease_snapshot_to_dict(load_lease_snapshot()))
 
 
 async def method_not_allowed(request: Request, _exc: Exception) -> Response:
@@ -175,6 +179,7 @@ def create_app() -> Starlette:
             Route("/audit", audit, methods=["GET"]),
             Route("/worktrees", worktrees, methods=["GET"]),
             Route("/leases", leases, methods=["GET"]),
+            Route("/api/leases", api_leases, methods=["GET"]),
         ],
         exception_handlers={405: method_not_allowed},
     )

webui/lease_loader.py

@@ -0,0 +1,330 @@
+"""Lease and collision visibility for the web UI (#433)."""
+
+from __future__ import annotations
+
+import os
+import re
+import subprocess
+from dataclasses import dataclass
+from typing import Any, Callable
+from urllib.parse import urlparse
+
+from gitea_auth import api_fetch_page, get_auth_header, repo_api_url
+from issue_claim_heartbeat import build_claim_inventory
+from merged_cleanup_reconcile import ISSUE_LOCK_FILE, read_issue_lock
+
+from webui.project_registry import ProjectRecord, load_registry
+from webui.queue_loader import _extract_linked_issue, _fetch_issues, _fetch_prs
+
+_REVIEWER_LEASE_MARKER = "<!-- mcp-review-lease:v1 -->"
+_REVIEWER_FIELD_RE = re.compile(
+    r"^\s*([a-z_]+)\s*:\s*(.+?)\s*$",
+    re.IGNORECASE | re.MULTILINE,
+)
+_ISSUE_BRANCH_RE = re.compile(r"issue-(\d+)", re.IGNORECASE)
+
+_COLLISION_HISTORY = (
+    {"number": 267, "title": "Author work leases"},
+    {"number": 268, "title": "Issue claim heartbeat leases"},
+    {"number": 400, "title": "Early duplicate-work detection"},
+    {"number": 407, "title": "Per-PR reviewer leases"},
+)
+
+
+@dataclass(frozen=True)
+class CollisionWarning:
+    kind: str
+    message: str
+    issue_number: int | None = None
+    pr_numbers: tuple[int, ...] = ()
+
+
+@dataclass(frozen=True)
+class LeaseSnapshot:
+    project_id: str
+    repo_label: str
+    issue_lock: dict[str, Any] | None
+    claim_inventory: dict[str, Any]
+    reviewer_leases: tuple[dict[str, Any], ...]
+    duplicate_prs: tuple[CollisionWarning, ...]
+    duplicate_branches: tuple[CollisionWarning, ...]
+    collision_history: tuple[dict[str, Any], ...]
+    fetch_error: str | None = None
+
+
+def _repo_root() -> str:
+    override = (os.environ.get("WEBUI_REPO_ROOT") or "").strip()
+    if override:
+        return os.path.realpath(override)
+    return os.path.realpath(os.path.join(os.path.dirname(__file__), ".."))
+
+
+def _host_from_url(remote_host: str) -> str:
+    parsed = urlparse(remote_host.strip())
+    return parsed.netloc or remote_host.strip().rstrip("/")
+
+
+def _parse_pr_ref(value: str | None) -> int | None:
+    digits = re.sub(r"[^\d]", "", value or "")
+    return int(digits) if digits.isdigit() else None
+
+
+def parse_reviewer_lease_comment(body: str) -> dict[str, Any] | None:
+    text = body or ""
+    if _REVIEWER_LEASE_MARKER not in text:
+        return None
+    fields: dict[str, str] = {}
+    for match in _REVIEWER_FIELD_RE.finditer(text):
+        fields[match.group(1).strip().lower()] = match.group(2).strip()
+    if not fields:
+        return None
+    return {
+        "pr_number": _parse_pr_ref(fields.get("pr")),
+        "issue_number": _parse_pr_ref(fields.get("issue")),
+        "reviewer_identity": fields.get("reviewer_identity"),
+        "profile": fields.get("profile"),
+        "phase": (fields.get("phase") or "").strip().lower() or None,
+        "expires_at": fields.get("expires_at"),
+        "blocker": fields.get("blocker"),
+    }
+
+
+def _fetch_comments(
+    host: str,
+    org: str,
+    repo: str,
+    auth: str,
+    *,
+    issue_number: int,
+) -> list[dict]:
+    url = f"{repo_api_url(host, org, repo)}/issues/{issue_number}/comments"
+    comments: list[dict] = []
+    page = 1
+    while page <= 10:
+        raw_page, meta = api_fetch_page(url, auth, page=page, limit=50)
+        comments.extend(raw_page)
+        if meta.get("is_final_page"):
+            break
+        page += 1
+    return comments
+
+
+def _list_local_branch_names(project_root: str) -> list[str]:
+    result = subprocess.run(
+        ["git", "-C", project_root, "branch", "--list", "--format=%(refname:short)"],
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+    if result.returncode != 0:
+        return []
+    return [line.strip() for line in (result.stdout or "").splitlines() if line.strip()]
+
+
+def _duplicate_pr_warnings(raw_prs: list[dict]) -> list[CollisionWarning]:
+    issue_to_prs: dict[int, list[int]] = {}
+    for pr in raw_prs:
+        linked = _extract_linked_issue(pr.get("title"), pr.get("body"))
+        if linked is None:
+            continue
+        issue_to_prs.setdefault(linked, []).append(int(pr["number"]))
+    warnings: list[CollisionWarning] = []
+    for issue_number, pr_numbers in sorted(issue_to_prs.items()):
+        if len(pr_numbers) > 1:
+            warnings.append(
+                CollisionWarning(
+                    kind="duplicate-pr",
+                    issue_number=issue_number,
+                    pr_numbers=tuple(sorted(pr_numbers)),
+                    message=(
+                        f"Issue #{issue_number} has {len(pr_numbers)} open PRs: "
+                        f"{', '.join(f'#{n}' for n in sorted(pr_numbers))} (#400)"
+                    ),
+                )
+            )
+    return warnings
+
+
+def _duplicate_branch_warnings(branch_names: list[str]) -> list[CollisionWarning]:
+    issue_to_branches: dict[int, list[str]] = {}
+    for name in branch_names:
+        match = _ISSUE_BRANCH_RE.search(name)
+        if not match:
+            continue
+        issue_num = int(match.group(1))
+        issue_to_branches.setdefault(issue_num, []).append(name)
+    warnings: list[CollisionWarning] = []
+    for issue_number, branches in sorted(issue_to_branches.items()):
+        if len(branches) > 1:
+            warnings.append(
+                CollisionWarning(
+                    kind="duplicate-branch",
+                    issue_number=issue_number,
+                    message=(
+                        f"Issue #{issue_number} has {len(branches)} local branches: "
+                        f"{', '.join(branches)}"
+                    ),
+                )
+            )
+    return warnings
+
+
+def _extract_reviewer_leases(
+    raw_prs: list[dict],
+    *,
+    fetch_comments: Callable[[int], list[dict]],
+) -> list[dict[str, Any]]:
+    leases: list[dict[str, Any]] = []
+    for pr in raw_prs:
+        pr_number = int(pr["number"])
+        for comment in fetch_comments(pr_number):
+            parsed = parse_reviewer_lease_comment(comment.get("body") or "")
+            if not parsed:
+                continue
+            leases.append(
+                {
+                    **parsed,
+                    "pr_number": parsed.get("pr_number") or pr_number,
+                    "comment_id": comment.get("id"),
+                    "author": (comment.get("user") or {}).get("login"),
+                    "created_at": comment.get("created_at"),
+                }
+            )
+    active_phases = {"claimed", "validating", "approved", "request-changes", "merging"}
+    return [lease for lease in leases if (lease.get("phase") or "") in active_phases]
+
+
+def load_lease_snapshot(
+    *,
+    project_id: str | None = None,
+    project_root: str | None = None,
+    issue_lock_path: str | None = None,
+    fetch_prs: Callable | None = None,
+    fetch_issues: Callable | None = None,
+    fetch_comments: Callable[[str, str, str, str, int], list[dict]] | None = None,
+) -> LeaseSnapshot:
+    registry = load_registry()
+    project: ProjectRecord | None = None
+    if project_id:
+        project = next((p for p in registry.projects if p.id == project_id), None)
+    else:
+        project = registry.projects[0] if registry.projects else None
+
+    root = project_root or _repo_root()
+    lock = read_issue_lock(issue_lock_path if issue_lock_path is not None else ISSUE_LOCK_FILE)
+
+    if project is None:
+        return LeaseSnapshot(
+            project_id=project_id or "",
+            repo_label="",
+            issue_lock=lock,
+            claim_inventory={"entries": [], "counts": {}},
+            reviewer_leases=(),
+            duplicate_prs=(),
+            duplicate_branches=(),
+            collision_history=_COLLISION_HISTORY,
+            fetch_error="project not found in registry",
+        )
+
+    host = _host_from_url(project.remote_host)
+    pr_fetch = fetch_prs or _fetch_prs
+    issue_fetch = fetch_issues or _fetch_issues
+    comment_fetch = fetch_comments or _fetch_comments
+    using_live = fetch_prs is None or fetch_issues is None
+    auth = get_auth_header(host) if using_live else "test-auth"
+
+    if using_live and not auth:
+        return LeaseSnapshot(
+            project_id=project.id,
+            repo_label=f"{project.gitea_owner}/{project.repo_name}",
+            issue_lock=lock,
+            claim_inventory={"entries": [], "counts": {}},
+            reviewer_leases=(),
+            duplicate_prs=(),
+            duplicate_branches=_duplicate_branch_warnings(_list_local_branch_names(root)),
+            collision_history=_COLLISION_HISTORY,
+            fetch_error=(
+                f"Gitea credentials unavailable for {host}; "
+                "remote lease artifacts cannot be loaded"
+            ),
+        )
+
+    try:
+        raw_prs, _ = pr_fetch(host, project.gitea_owner, project.repo_name, auth)
+        raw_issues, _ = issue_fetch(host, project.gitea_owner, project.repo_name, auth)
+    except Exception as exc:  # noqa: BLE001
+        return LeaseSnapshot(
+            project_id=project.id,
+            repo_label=f"{project.gitea_owner}/{project.repo_name}",
+            issue_lock=lock,
+            claim_inventory={"entries": [], "counts": {}},
+            reviewer_leases=(),
+            duplicate_prs=(),
+            duplicate_branches=_duplicate_branch_warnings(_list_local_branch_names(root)),
+            collision_history=_COLLISION_HISTORY,
+            fetch_error=f"Gitea fetch failed: {exc}",
+        )
+
+    comments_by_issue: dict[int, list[dict]] = {}
+    for issue in raw_issues:
+        if not any(lb.get("name") == "status:in-progress" for lb in issue.get("labels", [])):
+            continue
+        number = int(issue["number"])
+        comments_by_issue[number] = comment_fetch(
+            host, project.gitea_owner, project.repo_name, auth, issue_number=number
+        )
+
+    branch_names = _list_local_branch_names(root)
+    inventory = build_claim_inventory(
+        issues=raw_issues,
+        comments_by_issue=comments_by_issue,
+        open_prs=raw_prs,
+        branch_names=branch_names,
+    )
+
+    def _pr_comments(pr_number: int) -> list[dict]:
+        return comment_fetch(
+            host, project.gitea_owner, project.repo_name, auth, issue_number=pr_number
+        )
+
+    reviewer_leases = tuple(_extract_reviewer_leases(raw_prs, fetch_comments=_pr_comments))
+
+    return LeaseSnapshot(
+        project_id=project.id,
+        repo_label=f"{project.gitea_owner}/{project.repo_name}",
+        issue_lock=lock,
+        claim_inventory=inventory,
+        reviewer_leases=reviewer_leases,
+        duplicate_prs=tuple(_duplicate_pr_warnings(raw_prs)),
+        duplicate_branches=tuple(_duplicate_branch_warnings(branch_names)),
+        collision_history=_COLLISION_HISTORY,
+    )
+
+
+def snapshot_to_dict(snapshot: LeaseSnapshot) -> dict[str, Any]:
+    return {
+        "project_id": snapshot.project_id,
+        "repo_label": snapshot.repo_label,
+        "issue_lock": snapshot.issue_lock,
+        "claim_inventory": snapshot.claim_inventory,
+        "reviewer_leases": list(snapshot.reviewer_leases),
+        "duplicate_prs": [
+            {
+                "kind": w.kind,
+                "message": w.message,
+                "issue_number": w.issue_number,
+                "pr_numbers": list(w.pr_numbers),
+            }
+            for w in snapshot.duplicate_prs
+        ],
+        "duplicate_branches": [
+            {
+                "kind": w.kind,
+                "message": w.message,
+                "issue_number": w.issue_number,
+            }
+            for w in snapshot.duplicate_branches
+        ],
+        "collision_history": list(snapshot.collision_history),
+        "fetch_error": snapshot.fetch_error,
+    }

webui/lease_views.py

@@ -0,0 +1,130 @@
+"""HTML views for lease and collision visibility (#433)."""
+
+from __future__ import annotations
+
+import html
+import json
+
+from webui.layout import render_page
+from webui.lease_loader import LeaseSnapshot
+
+
+def _escape(text: str) -> str:
+    return html.escape(text, quote=True)
+
+
+def _warnings_block(snapshot: LeaseSnapshot) -> str:
+    warnings = list(snapshot.duplicate_prs) + list(snapshot.duplicate_branches)
+    if not warnings:
+        return "<p class='muted'>No duplicate PR/branch collisions detected in current inventory.</p>"
+    items = "".join(f"<li>{_escape(w.message)}</li>" for w in warnings)
+    return f"<ul class='collision-warnings'>{items}</ul>"
+
+
+def _lock_block(snapshot: LeaseSnapshot) -> str:
+    lock = snapshot.issue_lock
+    if not lock:
+        return "<p class='muted'>No active local issue lock file.</p>"
+    return (
+        "<pre class='prompt-text'>"
+        f"{_escape(json.dumps(lock, indent=2, sort_keys=True))}"
+        "</pre>"
+    )
+
+
+def _claims_table(snapshot: LeaseSnapshot) -> str:
+    entries = snapshot.claim_inventory.get("entries") or []
+    if not entries:
+        return "<p class='muted'>No in-progress issue claims in fetched inventory.</p>"
+    rows = []
+    for entry in entries:
+        rows.append(
+            "<tr>"
+            f"<td>#{entry.get('issue_number')}</td>"
+            f"<td><span class='badge badge-{_escape(str(entry.get('status')))}'>"
+            f"{_escape(str(entry.get('status')))}</span></td>"
+            f"<td>{_escape(str(entry.get('linked_open_pr') or '—'))}</td>"
+            f"<td>{entry.get('heartbeat_count', 0)}</td>"
+            f"<td>{_escape(', '.join(entry.get('matching_branches') or []) or '—')}</td>"
+            f"<td class='muted'>{_escape('; '.join(entry.get('reasons') or []))}</td>"
+            "</tr>"
+        )
+    return (
+        "<table class='registry leases'>"
+        "<thead><tr><th>Issue</th><th>Claim status</th><th>Open PR</th>"
+        "<th>Heartbeats</th><th>Branches</th><th>Notes</th></tr></thead>"
+        f"<tbody>{''.join(rows)}</tbody></table>"
+    )
+
+
+def _reviewer_leases_table(snapshot: LeaseSnapshot) -> str:
+    if not snapshot.reviewer_leases:
+        return (
+            "<p class='muted'>No active reviewer PR lease comments found "
+            "(marker <code>&lt;!-- mcp-review-lease:v1 --&gt;</code>; see #407).</p>"
+        )
+    rows = []
+    for lease in snapshot.reviewer_leases:
+        rows.append(
+            "<tr>"
+            f"<td>#{lease.get('pr_number')}</td>"
+            f"<td>{_escape(str(lease.get('reviewer_identity') or '—'))}</td>"
+            f"<td><code>{_escape(str(lease.get('profile') or '—'))}</code></td>"
+            f"<td>{_escape(str(lease.get('phase') or '—'))}</td>"
+            f"<td><code>{_escape(str(lease.get('expires_at') or '—'))}</code></td>"
+            "</tr>"
+        )
+    return (
+        "<table class='registry leases'>"
+        "<thead><tr><th>PR</th><th>Reviewer</th><th>Profile</th>"
+        "<th>Phase</th><th>Expires</th></tr></thead>"
+        f"<tbody>{''.join(rows)}</tbody></table>"
+    )
+
+
+def _history_links(snapshot: LeaseSnapshot) -> str:
+    items = "".join(
+        f"<li><a href=\"https://gitea.prgs.cc/Scaled-Tech-Consulting/Gitea-Tools/issues/"
+        f"{item['number']}\">#{item['number']}</a> — {_escape(item['title'])}</li>"
+        for item in snapshot.collision_history
+    )
+    return f"<ul>{items}</ul>"
+
+
+LEASE_PAGE_STYLES = """
+<style>
+  .collision-warnings li { color: #f0c4c4; margin: 0.35rem 0; }
+  table.leases td:nth-child(6) { font-size: 0.85rem; }
+  .badge-active, .badge-awaiting_review { color: #8fd19e; border-color: #3d6b4a; }
+  .badge-stale, .badge-phantom, .badge-reclaimable { color: #f0a8a8; border-color: #7a3b3b; }
+</style>
+"""
+
+
+def render_leases_page(snapshot: LeaseSnapshot) -> str:
+    error_block = ""
+    if snapshot.fetch_error:
+        error_block = (
+            '<div class="stub"><p><strong>Partial load:</strong> '
+            f"{_escape(snapshot.fetch_error)}</p></div>"
+        )
+    body = (
+        "<h2>Leases &amp; collisions</h2>"
+        "<p>Read-only visibility for issue claims, reviewer PR leases, and "
+        "duplicate-work risks. Does not acquire or release leases.</p>"
+        f"{error_block}"
+        f"<p class='meta'>Project: <code>{_escape(snapshot.repo_label)}</code></p>"
+        "<h3>Collision warnings</h3>"
+        f"{_warnings_block(snapshot)}"
+        "<h3>Local issue lock</h3>"
+        f"{_lock_block(snapshot)}"
+        "<h3>In-progress issue claims (#268)</h3>"
+        f"{_claims_table(snapshot)}"
+        "<h3>Reviewer PR leases (#407)</h3>"
+        f"{_reviewer_leases_table(snapshot)}"
+        "<h3>Collision / lease history issues</h3>"
+        f"{_history_links(snapshot)}"
+        "<p><a href=\"/api/leases\">JSON API</a></p>"
+        f"{LEASE_PAGE_STYLES}"
+    )
+    return render_page(title="Leases", body_html=body)