feat(v0.6): per-project detail view — branch/worktrees + active sessions

Clicking a project's name opens an in-app detail view (back button returns to
the grid) with:
- header: name, path, branch, dirty
- Branch / Worktrees: each `git worktree list` entry (branch or detached@head,
  main/current/locked/prunable tags, path) — a single-worktree repo shows its
  branch; a multi-worktree repo shows them all
- Active sessions (N): detailed rows (status, devices watching, started-ago)
  with Open + Kill
- the Claude/Codex/VS Code launcher row

Backend: src/http/worktrees.ts (parseWorktrees pure + listWorktrees via
execFile, no shell, best-effort); buildProjectDetail(cfg, path, liveSessions)
in projects.ts (validates absolute existing dir, reuses branch/dirty/session
helpers, uncached — detail is on-demand and wants fresh state); read-only
GET /projects/detail?path= (no Origin guard, like /projects; 400 missing /
404 invalid). Types: WorktreeInfo, ProjectDetail.

Frontend: detail view + navigation in projects.ts (grid<->detail), project
name becomes a link, Kill via DELETE /live-sessions/:id.

Tests +21 (452 total): worktree parser, buildProjectDetail (validation,
non-git, session merge, real git-init worktree), renderProjectDetail.
worktrees.ts 100% / projects.ts 93.8% cov. Verified in-browser: opened a
Claude session, then the detail showed its branch+worktree and the live
session with Open/Kill.

public/projects.ts

@@ -13,8 +13,14 @@
  * stopped + cleaned up on hide.
  */
 
-import type { ProjectInfo, ProjectSessionRef, ClaudeStatus } from '../src/types.js'
-import { el, relTime } from './preview-grid.js'
+import type {
+  ProjectInfo,
+  ProjectSessionRef,
+  ClaudeStatus,
+  ProjectDetail,
+  WorktreeInfo,
+} from '../src/types.js'
+import { el, relTime, statusText } from './preview-grid.js'
 import { CLAUDE_LOGO, CODEX_LOGO, VSCODE_LOGO } from './icons.js'
 
 /* ── Constants ───────────────────────────────────────────────────────────── */
@@ -137,6 +143,26 @@ async function fetchProjects(): Promise<ProjectInfo[]> {
   }
 }
 
+/** Fetch one project's detail (branch/worktrees + sessions). null on any error. */
+async function fetchProjectDetail(projectPath: string): Promise<ProjectDetail | null> {
+  try {
+    const res = await fetch(`/projects/detail?path=${encodeURIComponent(projectPath)}`)
+    if (!res.ok) return null
+    return (await res.json()) as ProjectDetail
+  } catch {
+    return null
+  }
+}
+
+/** Kill a running session (manage-page DELETE; same-origin → Origin guard passes). */
+async function killSession(id: string): Promise<void> {
+  try {
+    await fetch(`/live-sessions/${encodeURIComponent(id)}`, { method: 'DELETE' })
+  } catch {
+    // best-effort — the refresh that follows will reflect the real state
+  }
+}
+
 /* ── Status helpers ──────────────────────────────────────────────────────── */
 
 function sessionDotClass(status: ClaudeStatus): string {
@@ -256,6 +282,7 @@ export function makeProjectCard(
   favs: ReadonlySet<string>,
   hooks: ProjectsHooks,
   onToggleFav: (path: string) => void,
+  onOpenDetail?: (path: string) => void,
 ): HTMLElement {
   const card = el('div', 'proj-card')
 
@@ -272,6 +299,19 @@ export function makeProjectCard(
   })
 
   const name = el('span', 'proj-name', project.name)
+  if (onOpenDetail) {
+    name.classList.add('proj-name-link')
+    name.setAttribute('role', 'button')
+    name.tabIndex = 0
+    name.title = `View ${project.name} details`
+    name.addEventListener('click', () => onOpenDetail(project.path))
+    name.addEventListener('keydown', (e) => {
+      if (e.key === 'Enter' || e.key === ' ') {
+        e.preventDefault()
+        onOpenDetail(project.path)
+      }
+    })
+  }
 
   header.append(favBtn, name)
 
@@ -310,6 +350,112 @@ export function makeProjectCard(
   return card
 }
 
+/* ── Detail view (branch / worktrees + active sessions) ─────────────────────── */
+
+/** One worktree row: branch (or detached@head) + main/current/locked tags + path. */
+function makeWorktreeRow(wt: WorktreeInfo): HTMLElement {
+  const row = el('div', 'proj-wt-row')
+  const label = wt.branch ?? (wt.head ? `detached @ ${wt.head}` : 'detached')
+  row.append(el('span', 'proj-wt-branch', label))
+  if (wt.isMain) row.append(el('span', 'proj-wt-tag', 'main'))
+  if (wt.isCurrent) row.append(el('span', 'proj-wt-tag proj-wt-tag-current', 'current'))
+  if (wt.locked) row.append(el('span', 'proj-wt-tag', 'locked'))
+  if (wt.prunable) row.append(el('span', 'proj-wt-tag', 'prunable'))
+  row.append(el('span', 'proj-wt-path', wt.path))
+  return row
+}
+
+/** One detailed session row: status + title + metadata + Open / Kill actions. */
+function makeDetailSessionRow(
+  s: ProjectSessionRef,
+  onEnter: (id: string) => void,
+  onKill: (id: string) => void,
+): HTMLElement {
+  const row = el('div', 'proj-dsession')
+  const dot = el('span', sessionDotClass(s.status))
+  const main = el('div', 'proj-dsession-main')
+  main.append(el('span', 'proj-dsession-title', s.title ?? 'session'))
+  const parts: string[] = []
+  if (s.status !== 'unknown') parts.push(statusText(s.status))
+  parts.push(`👁 ${s.clientCount}`)
+  parts.push(`started ${relTime(s.createdAt)} ago`)
+  main.append(el('span', 'proj-dsession-meta', parts.join(' · ')))
+  const open = el('button', 'proj-dsession-open', 'Open')
+  open.addEventListener('click', () => onEnter(s.id))
+  const kill = el('button', 'proj-dsession-kill', '✕')
+  kill.title = 'Kill this session'
+  kill.setAttribute('aria-label', 'Kill session')
+  kill.addEventListener('click', () => onKill(s.id))
+  row.append(dot, main, open, kill)
+  return row
+}
+
+interface DetailCallbacks {
+  onBack: () => void
+  onKill: (id: string) => void
+}
+
+/** Render the project detail view (exported for unit tests). */
+export function renderProjectDetail(
+  detail: ProjectDetail | null,
+  hooks: ProjectsHooks,
+  cb: DetailCallbacks,
+): HTMLElement {
+  const root = el('div', 'proj-detail-inner')
+
+  const back = el('button', 'proj-back', '← All projects')
+  back.addEventListener('click', () => cb.onBack())
+  root.append(back)
+
+  if (detail === null) {
+    root.append(el('div', 'proj-empty', 'Project not found.'))
+    return root
+  }
+
+  // Header: name + branch + dirty + path
+  const head = el('div', 'proj-detail-head')
+  head.append(el('h2', 'proj-detail-name', detail.name))
+  if (detail.branch) head.append(el('span', 'proj-branch', detail.branch))
+  if (detail.dirty === true) {
+    const d = el('span', 'proj-dirty', '●')
+    d.title = 'Uncommitted changes'
+    head.append(d)
+  }
+  root.append(head)
+  root.append(el('div', 'proj-detail-path', detail.path))
+
+  // Branch / worktrees
+  root.append(el('div', 'proj-section-title', detail.worktrees.length > 1 ? 'Worktrees' : 'Branch'))
+  if (!detail.isGit) {
+    root.append(el('div', 'proj-empty', 'Not a git repository.'))
+  } else if (detail.worktrees.length === 0) {
+    root.append(
+      el('div', 'proj-empty', detail.branch ? `On branch ${detail.branch}` : 'No worktree info.'),
+    )
+  } else {
+    const list = el('div', 'proj-wt-list')
+    for (const wt of detail.worktrees) list.append(makeWorktreeRow(wt))
+    root.append(list)
+  }
+
+  // Active sessions
+  const running = detail.sessions.filter((s) => !s.exited)
+  root.append(el('div', 'proj-section-title', `Active sessions (${running.length})`))
+  if (running.length === 0) {
+    root.append(el('div', 'proj-empty', 'No running sessions — start one below.'))
+  } else {
+    const list = el('div', 'proj-detail-sessions')
+    for (const s of running) list.append(makeDetailSessionRow(s, hooks.onEnterSession, cb.onKill))
+    root.append(list)
+  }
+
+  // Launchers
+  root.append(el('div', 'proj-section-title', 'Start'))
+  root.append(makeLauncherRow(detail, hooks))
+
+  return root
+}
+
 /* ── Mount ───────────────────────────────────────────────────────────────── */
 
 export function mountProjects(host: HTMLElement, hooks: ProjectsHooks): ProjectsPanel {
@@ -330,9 +476,36 @@ export function mountProjects(host: HTMLElement, hooks: ProjectsHooks): Projects
   const grid = el('div', 'proj-grid')
   root.append(grid)
 
+  const detailEl = el('div', 'proj-detail')
+  detailEl.style.display = 'none'
+  root.append(detailEl)
+
   let allProjects: ProjectInfo[] = []
   let favs: Set<string> = getFavs()
   let timer: ReturnType<typeof setInterval> | null = null
+  let view: 'grid' | 'detail' = 'grid'
+  let detailPath: string | null = null
+
+  function applyView(): void {
+    const isGrid = view === 'grid'
+    searchWrap.style.display = isGrid ? '' : 'none'
+    grid.style.display = isGrid ? '' : 'none'
+    detailEl.style.display = isGrid ? 'none' : 'block'
+  }
+
+  function openDetail(p: string): void {
+    view = 'detail'
+    detailPath = p
+    applyView()
+    void refresh()
+  }
+
+  function closeDetail(): void {
+    view = 'grid'
+    detailPath = null
+    applyView()
+    void refresh()
+  }
 
   function renderGrid(): void {
     const filtered = filterProjects(allProjects, searchInput.value)
@@ -351,16 +524,39 @@ export function mountProjects(host: HTMLElement, hooks: ProjectsHooks): Projects
 
     for (const p of sorted) {
       grid.append(
-        makeProjectCard(p, favs, hooks, (path) => {
-          favs = toggleFav(favs, path)
-          saveFavs(favs)
-          renderGrid()
-        }),
+        makeProjectCard(
+          p,
+          favs,
+          hooks,
+          (path) => {
+            favs = toggleFav(favs, path)
+            saveFavs(favs)
+            renderGrid()
+          },
+          openDetail,
+        ),
       )
     }
   }
 
+  function renderDetail(detail: ProjectDetail | null): void {
+    detailEl.replaceChildren(
+      renderProjectDetail(detail, hooks, {
+        onBack: closeDetail,
+        onKill: (id) => {
+          void killSession(id).then(() => {
+            if (view === 'detail') void refresh()
+          })
+        },
+      }),
+    )
+  }
+
   async function refresh(): Promise<void> {
+    if (view === 'detail' && detailPath !== null) {
+      renderDetail(await fetchProjectDetail(detailPath))
+      return
+    }
     allProjects = await fetchProjects()
     favs = getFavs()
     renderGrid()
@@ -372,6 +568,10 @@ export function mountProjects(host: HTMLElement, hooks: ProjectsHooks): Projects
     setVisible(v: boolean): void {
       root.style.display = v ? 'block' : 'none'
       if (v) {
+        // Re-entering the chooser always lands on the grid (never a stale detail).
+        view = 'grid'
+        detailPath = null
+        applyView()
         void refresh()
         if (timer === null) {
           timer = setInterval(() => {