feat: activity sidecar edits via bincio edit --serve

- bincio/render/merge.py: parse sidecar .md files (YAML frontmatter +
     markdown body), produce data/_merged/ with symlinks for unmodified
     activities and real merged files for overridden ones; filters private
     activities from index.json; sorts highlighted activities first.
     Keeps extracted data pristine — re-running extract never clobbers edits.

   - bincio/edit/: FastAPI edit server (port 4041) with embedded HTML/JS
     edit UI; GET/POST /api/activity/{id} reads/writes sidecars; multipart
     image upload to edits/images/{id}/; DELETE for image cleanup.

   - bincio render now calls merge_all() before build/serve and symlinks
     public/data → data/_merged/ instead of data/ directly.

   - ActivityDetail.svelte: edit button (links to edit server) when
     PUBLIC_EDIT_URL env var is set; respects custom.hide_stats to suppress
     stat panels; description supports whitespace-preserving rendering.

   - 15 unit tests covering parse_sidecar, apply_sidecar, and merge_all.

bincio/cli.py

@@ -13,6 +13,8 @@ def main() -> None:
 
 from bincio.extract.cli import extract  # noqa: E402
 from bincio.render.cli import render  # noqa: E402
+from bincio.edit.cli import edit  # noqa: E402
 
 main.add_command(extract)
 main.add_command(render)
+main.add_command(edit)

bincio/edit/cli.py

@@ -0,0 +1,79 @@
+"""bincio edit — local edit server for activity sidecar files."""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Optional
+
+import click
+from rich.console import Console
+
+console = Console()
+
+
+@click.command()
+@click.option("--data-dir", default=None,
+              help="BAS data store directory (output of bincio extract).")
+@click.option("--port", default=4041, show_default=True,
+              help="Port for the edit server.")
+@click.option("--site-url", default="http://localhost:4321", show_default=True,
+              help="URL of the Astro dev server (for the Back link).")
+@click.option("--config", "config_path", default=None,
+              help="Path to extract_config.yaml (reads output.dir from it).")
+def edit(
+    data_dir: Optional[str],
+    port: int,
+    site_url: str,
+    config_path: Optional[str],
+) -> None:
+    """Start a local web UI for editing activity sidecar files.
+
+    Writes sidecar .md files to <data-dir>/edits/ which bincio render picks
+    up and applies at build time.
+
+    Run alongside the Astro dev server:
+
+    \b
+        bincio render --serve      # port 4321  (or npm run dev)
+        bincio edit                # port 4041
+    """
+    try:
+        import uvicorn
+    except ImportError:
+        raise click.ClickException(
+            "uvicorn is required for the edit server.\n"
+            "Install with: uv add 'bincio[edit]'"
+        )
+
+    data = _resolve_data_dir(data_dir, config_path)
+    console.print(f"Data dir: [cyan]{data}[/cyan]")
+    console.print(f"Edit UI:  [cyan]http://localhost:{port}/edit/<activity-id>[/cyan]")
+    console.print(f"Site URL: [cyan]{site_url}[/cyan]")
+    console.print("Press [bold]Ctrl+C[/bold] to stop.\n")
+
+    import bincio.edit.server as srv
+    srv.data_dir = data
+    srv.site_url = site_url
+
+    uvicorn.run(srv.app, host="127.0.0.1", port=port, log_level="warning")
+
+
+def _resolve_data_dir(explicit: Optional[str], config_path: Optional[str]) -> Path:
+    if explicit:
+        return Path(explicit).expanduser().resolve()
+
+    if config_path and Path(config_path).exists():
+        import yaml
+        raw = yaml.safe_load(Path(config_path).read_text())
+        out = raw.get("output", {}).get("dir")
+        if out:
+            return Path(out).expanduser().resolve()
+
+    default = Path.cwd() / "bincio_data"
+    if default.exists():
+        return default
+
+    raise click.UsageError(
+        "Could not find the BAS data directory. "
+        "Run `bincio extract` first, or pass --data-dir."
+    )

bincio/edit/server.py

@@ -0,0 +1,433 @@
+"""FastAPI edit server — serves the activity edit UI and writes sidecar .md files."""
+
+from __future__ import annotations
+
+import json
+import shutil
+from pathlib import Path
+from typing import Any
+
+from fastapi import FastAPI, File, HTTPException, UploadFile
+from fastapi.responses import HTMLResponse, JSONResponse, RedirectResponse
+
+# Populated by the CLI before uvicorn starts
+data_dir: Path | None = None
+site_url: str = "http://localhost:4321"
+
+app = FastAPI(title="BincioActivity Edit Server", docs_url=None, redoc_url=None)
+
+SPORTS = ["cycling", "running", "hiking", "walking", "swimming", "skiing", "other"]
+STAT_PANELS = ["elevation", "speed", "heart_rate", "cadence", "power"]
+
+
+# ── HTML UI ───────────────────────────────────────────────────────────────────
+
+_HTML = """\
+<!DOCTYPE html>
+<html lang="en">
+<head>
+<meta charset="UTF-8">
+<meta name="viewport" content="width=device-width, initial-scale=1.0">
+<title>Edit Activity</title>
+<style>
+*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
+:root {
+  --bg: #09090b; --surface: #18181b; --border: #27272a;
+  --text: #fafafa; --muted: #71717a; --accent: #3b82f6;
+  --accent-dim: #1d3461; --danger: #ef4444;
+  --radius: 10px; --font: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
+}
+body { background: var(--bg); color: var(--text); font-family: var(--font);
+  font-size: 14px; line-height: 1.5; padding: 24px; min-height: 100vh; }
+a { color: var(--accent); text-decoration: none; }
+a:hover { text-decoration: underline; }
+h1 { font-size: 1.25rem; font-weight: 700; }
+label { display: block; font-size: 12px; color: var(--muted); margin-bottom: 4px; }
+input, select, textarea {
+  width: 100%; padding: 8px 12px; background: var(--surface); border: 1px solid var(--border);
+  border-radius: 6px; color: var(--text); font-size: 14px; font-family: var(--font);
+  outline: none; transition: border-color .15s;
+}
+input:focus, select:focus, textarea:focus { border-color: var(--accent); }
+textarea { resize: vertical; min-height: 140px; }
+.field { margin-bottom: 16px; }
+.row { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
+.check-group { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 4px; }
+.check-item { display: flex; align-items: center; gap: 6px; cursor: pointer;
+  padding: 6px 10px; border: 1px solid var(--border); border-radius: 6px;
+  user-select: none; transition: border-color .15s, background .15s; }
+.check-item:hover { border-color: var(--muted); }
+.check-item input[type=checkbox] { width: auto; accent-color: var(--accent); }
+.check-item.active { border-color: var(--accent); background: var(--accent-dim); }
+.toggle-row { display: flex; gap: 16px; }
+.toggle { display: flex; align-items: center; gap: 8px; cursor: pointer;
+  padding: 6px 12px; border: 1px solid var(--border); border-radius: 6px;
+  transition: border-color .15s, background .15s; }
+.toggle:hover { border-color: var(--muted); }
+.toggle.active { border-color: var(--accent); background: var(--accent-dim); }
+.toggle input { width: auto; accent-color: var(--accent); }
+.drop-zone { border: 2px dashed var(--border); border-radius: var(--radius);
+  padding: 24px; text-align: center; color: var(--muted); cursor: pointer;
+  transition: border-color .15s; margin-top: 4px; }
+.drop-zone:hover, .drop-zone.drag-over { border-color: var(--accent); color: var(--text); }
+.image-list { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 10px; }
+.image-chip { display: flex; align-items: center; gap: 6px; padding: 4px 10px;
+  background: var(--surface); border: 1px solid var(--border); border-radius: 20px;
+  font-size: 12px; }
+.image-chip button { background: none; border: none; color: var(--muted);
+  cursor: pointer; font-size: 14px; line-height: 1; padding: 0 2px; }
+.image-chip button:hover { color: var(--danger); }
+.actions { display: flex; gap: 12px; align-items: center; margin-top: 8px; }
+.btn { padding: 8px 20px; border-radius: 6px; font-size: 14px; font-weight: 500;
+  cursor: pointer; border: none; transition: opacity .15s; }
+.btn:disabled { opacity: .4; cursor: default; }
+.btn-primary { background: var(--accent); color: #fff; }
+.btn-primary:hover:not(:disabled) { opacity: .85; }
+.btn-ghost { background: transparent; border: 1px solid var(--border); color: var(--text); }
+.btn-ghost:hover:not(:disabled) { border-color: var(--muted); }
+.status { font-size: 13px; }
+.status.ok { color: #4ade80; }
+.status.err { color: var(--danger); }
+.header { display: flex; align-items: baseline; gap: 16px; margin-bottom: 24px; }
+.back { font-size: 13px; color: var(--muted); }
+.meta { font-size: 12px; color: var(--muted); margin-top: 4px; }
+.card { background: var(--surface); border: 1px solid var(--border);
+  border-radius: var(--radius); padding: 20px; max-width: 780px; margin: 0 auto; }
+.section-title { font-size: 11px; text-transform: uppercase; letter-spacing: .08em;
+  color: var(--muted); margin-bottom: 14px; padding-bottom: 6px;
+  border-bottom: 1px solid var(--border); }
+</style>
+</head>
+<body>
+<div style="max-width:780px;margin:0 auto">
+  <div class="header">
+    <a class="back" href="__SITE_URL__">← Back to site</a>
+    <h1 id="page-title">Edit Activity</h1>
+  </div>
+  <p id="meta" class="meta" style="margin-bottom:16px"></p>
+
+  <div class="card">
+    <form id="form" autocomplete="off">
+      <p class="section-title">Identity</p>
+      <div class="row">
+        <div class="field">
+          <label for="title">Title</label>
+          <input id="title" name="title" type="text" placeholder="Leave blank to keep extracted title">
+        </div>
+        <div class="field">
+          <label for="sport">Sport</label>
+          <select id="sport" name="sport">
+            __SPORT_OPTIONS__
+          </select>
+        </div>
+      </div>
+      <div class="field">
+        <label for="gear">Gear</label>
+        <input id="gear" name="gear" type="text" placeholder="e.g. Trek Domane SL6">
+      </div>
+
+      <p class="section-title" style="margin-top:20px">Description</p>
+      <div class="field">
+        <label for="description">Markdown supported</label>
+        <textarea id="description" name="description" placeholder="Write about this activity…"></textarea>
+      </div>
+
+      <p class="section-title" style="margin-top:20px">Display</p>
+      <div class="field">
+        <label>Hide stat panels</label>
+        <div class="check-group" id="hide-stats-group">
+          __STAT_CHECKBOXES__
+        </div>
+      </div>
+      <div class="field" style="margin-top:12px">
+        <label>Flags</label>
+        <div class="toggle-row">
+          <label class="toggle" id="toggle-highlight">
+            <input type="checkbox" id="highlight" name="highlight"> Highlight in feed
+          </label>
+          <label class="toggle" id="toggle-private">
+            <input type="checkbox" id="private" name="private"> Private (hide from feed)
+          </label>
+        </div>
+      </div>
+
+      <p class="section-title" style="margin-top:20px">Images</p>
+      <div class="field">
+        <label>Drag & drop images or click to browse</label>
+        <div class="drop-zone" id="drop-zone">
+          <span id="drop-label">Drop images here or click to upload</span>
+          <input type="file" id="file-input" accept="image/*" multiple style="display:none">
+        </div>
+        <div class="image-list" id="image-list"></div>
+      </div>
+
+      <div class="actions">
+        <button type="submit" class="btn btn-primary" id="save-btn">Save</button>
+        <span class="status" id="status"></span>
+      </div>
+    </form>
+  </div>
+</div>
+
+<script>
+const id = location.pathname.split('/edit/')[1];
+const api = '/api/activity/' + id;
+let uploadedImages = [];
+
+// Fetch current data
+fetch(api).then(r => r.json()).then(data => {
+  document.getElementById('page-title').textContent = 'Edit: ' + (data.title || id);
+  document.getElementById('meta').textContent = data.started_at
+    ? new Date(data.started_at).toLocaleString() : '';
+  document.getElementById('title').value = data.title || '';
+  document.getElementById('sport').value = data.sport || 'other';
+  document.getElementById('gear').value = data.gear || '';
+  document.getElementById('description').value = data.description || '';
+  if (data.highlight) setToggle('highlight', true);
+  if (data.private) setToggle('private', true);
+  (data.hide_stats || []).forEach(s => {
+    const cb = document.querySelector(`input[data-stat="${s}"]`);
+    if (cb) { cb.checked = true; cb.closest('.check-item').classList.add('active'); }
+  });
+  uploadedImages = data.images || [];
+  renderImageList();
+}).catch(() => {
+  document.getElementById('status').textContent = 'Could not load activity data.';
+  document.getElementById('status').className = 'status err';
+});
+
+// Toggle active class on check items
+document.querySelectorAll('.check-item input[type=checkbox]').forEach(cb => {
+  cb.addEventListener('change', () => {
+    cb.closest('.check-item').classList.toggle('active', cb.checked);
+  });
+});
+
+function setToggle(name, val) {
+  const cb = document.getElementById(name);
+  cb.checked = val;
+  document.getElementById('toggle-' + name).classList.toggle('active', val);
+}
+document.getElementById('highlight').addEventListener('change', e => {
+  document.getElementById('toggle-highlight').classList.toggle('active', e.target.checked);
+});
+document.getElementById('private').addEventListener('change', e => {
+  document.getElementById('toggle-private').classList.toggle('active', e.target.checked);
+});
+
+// Image upload
+const dropZone = document.getElementById('drop-zone');
+const fileInput = document.getElementById('file-input');
+
+dropZone.addEventListener('click', () => fileInput.click());
+dropZone.addEventListener('dragover', e => { e.preventDefault(); dropZone.classList.add('drag-over'); });
+dropZone.addEventListener('dragleave', () => dropZone.classList.remove('drag-over'));
+dropZone.addEventListener('drop', e => {
+  e.preventDefault();
+  dropZone.classList.remove('drag-over');
+  uploadFiles([...e.dataTransfer.files]);
+});
+fileInput.addEventListener('change', () => uploadFiles([...fileInput.files]));
+
+async function uploadFiles(files) {
+  for (const file of files) {
+    const fd = new FormData();
+    fd.append('file', file);
+    const r = await fetch(api + '/images', { method: 'POST', body: fd });
+    if (r.ok) {
+      const d = await r.json();
+      if (!uploadedImages.includes(d.filename)) uploadedImages.push(d.filename);
+      renderImageList();
+      // Insert markdown image reference at end of description
+      const ta = document.getElementById('description');
+      const ref = '\\n![' + d.filename.replace(/\\.[^.]+$/, '') + '](' + d.filename + ')';
+      ta.value = ta.value.trimEnd() + ref;
+    }
+  }
+}
+
+function renderImageList() {
+  const list = document.getElementById('image-list');
+  list.innerHTML = uploadedImages.map(f =>
+    `<span class="image-chip">${f}
+      <button type="button" onclick="removeImage('${f}')" title="Remove">×</button>
+    </span>`
+  ).join('');
+}
+
+async function removeImage(filename) {
+  await fetch(api + '/images/' + encodeURIComponent(filename), { method: 'DELETE' });
+  uploadedImages = uploadedImages.filter(f => f !== filename);
+  renderImageList();
+}
+
+// Save
+document.getElementById('form').addEventListener('submit', async e => {
+  e.preventDefault();
+  const btn = document.getElementById('save-btn');
+  const status = document.getElementById('status');
+  btn.disabled = true;
+  status.textContent = 'Saving…';
+  status.className = 'status';
+
+  const hideStats = [...document.querySelectorAll('input[data-stat]:checked')]
+    .map(cb => cb.dataset.stat);
+
+  const payload = {
+    title: document.getElementById('title').value.trim(),
+    sport: document.getElementById('sport').value,
+    gear: document.getElementById('gear').value.trim(),
+    description: document.getElementById('description').value.trim(),
+    highlight: document.getElementById('highlight').checked,
+    private: document.getElementById('private').checked,
+    hide_stats: hideStats,
+  };
+
+  try {
+    const r = await fetch(api, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify(payload),
+    });
+    if (!r.ok) throw new Error(await r.text());
+    status.textContent = 'Saved! Re-run `bincio render` to rebuild.';
+    status.className = 'status ok';
+  } catch (err) {
+    status.textContent = 'Error: ' + err.message;
+    status.className = 'status err';
+  } finally {
+    btn.disabled = false;
+  }
+});
+</script>
+</body>
+</html>
+"""
+
+# ── Routes ────────────────────────────────────────────────────────────────────
+
+
+def _get_data_dir() -> Path:
+    if data_dir is None:
+        raise HTTPException(500, "Edit server not configured (data_dir is None)")
+    return data_dir
+
+
+@app.get("/")
+async def root() -> RedirectResponse:
+    return RedirectResponse(url=site_url)
+
+
+@app.get("/edit/{activity_id}", response_class=HTMLResponse)
+async def edit_page(activity_id: str) -> str:
+    sport_opts = "\n".join(
+        f'<option value="{s}">{s.capitalize()}</option>' for s in SPORTS
+    )
+    stat_cbs = "\n".join(
+        f'<label class="check-item"><input type="checkbox" data-stat="{s}"> {s.replace("_", " ").capitalize()}</label>'
+        for s in STAT_PANELS
+    )
+    html = (
+        _HTML
+        .replace("__SITE_URL__", site_url)
+        .replace("__SPORT_OPTIONS__", sport_opts)
+        .replace("__STAT_CHECKBOXES__", stat_cbs)
+    )
+    return html
+
+
+@app.get("/api/activity/{activity_id}")
+async def get_activity(activity_id: str) -> JSONResponse:
+    dd = _get_data_dir()
+    json_path = dd / "activities" / f"{activity_id}.json"
+    if not json_path.exists():
+        raise HTTPException(404, f"Activity {activity_id!r} not found")
+
+    detail: dict[str, Any] = json.loads(json_path.read_text(encoding="utf-8"))
+
+    # Read existing sidecar if any — these are the "user" values shown in the form
+    from bincio.render.merge import parse_sidecar
+    sidecar_path = dd / "edits" / f"{activity_id}.md"
+    fm: dict = {}
+    body = ""
+    if sidecar_path.exists():
+        fm, body = parse_sidecar(sidecar_path)
+
+    # Existing uploaded images for this activity
+    images_dir = dd / "edits" / "images" / activity_id
+    images = sorted(p.name for p in images_dir.iterdir() if p.is_file()) if images_dir.exists() else []
+
+    return JSONResponse({
+        "id": activity_id,
+        "started_at": detail.get("started_at", ""),
+        "title": fm.get("title", detail.get("title", "")),
+        "sport": fm.get("sport", detail.get("sport", "other")),
+        "gear": fm.get("gear", detail.get("gear") or ""),
+        "description": body or fm.get("description") or detail.get("description") or "",
+        "highlight": fm.get("highlight", detail.get("custom", {}).get("highlight", False)),
+        "private": fm.get("private", detail.get("privacy") == "private"),
+        "hide_stats": fm.get("hide_stats", detail.get("custom", {}).get("hide_stats", [])),
+        "images": images,
+    })
+
+
+@app.post("/api/activity/{activity_id}")
+async def save_activity(activity_id: str, payload: dict[str, Any]) -> JSONResponse:
+    dd = _get_data_dir()
+    if not (dd / "activities" / f"{activity_id}.json").exists():
+        raise HTTPException(404, f"Activity {activity_id!r} not found")
+
+    edits_dir = dd / "edits"
+    edits_dir.mkdir(exist_ok=True)
+    sidecar_path = edits_dir / f"{activity_id}.md"
+
+    lines: list[str] = []
+    if payload.get("title"):
+        lines.append(f"title: {json.dumps(payload['title'])}")
+    if payload.get("sport") and payload["sport"] != "other":
+        lines.append(f"sport: {payload['sport']}")
+    if payload.get("gear"):
+        lines.append(f"gear: {json.dumps(payload['gear'])}")
+    if payload.get("highlight"):
+        lines.append("highlight: true")
+    if payload.get("private"):
+        lines.append("private: true")
+    hide = payload.get("hide_stats") or []
+    if hide:
+        lines.append(f"hide_stats: [{', '.join(str(s) for s in hide)}]")
+
+    description = (payload.get("description") or "").strip()
+
+    content = "---\n" + "\n".join(lines) + "\n---\n"
+    if description:
+        content += "\n" + description + "\n"
+
+    sidecar_path.write_text(content, encoding="utf-8")
+    return JSONResponse({"ok": True, "sidecar": str(sidecar_path)})
+
+
+@app.post("/api/activity/{activity_id}/images")
+async def upload_image(activity_id: str, file: UploadFile = File(...)) -> JSONResponse:
+    dd = _get_data_dir()
+    if not (dd / "activities" / f"{activity_id}.json").exists():
+        raise HTTPException(404, f"Activity {activity_id!r} not found")
+    if not file.filename:
+        raise HTTPException(400, "No filename")
+
+    images_dir = dd / "edits" / "images" / activity_id
+    images_dir.mkdir(parents=True, exist_ok=True)
+    dest = images_dir / Path(file.filename).name
+    dest.write_bytes(await file.read())
+    return JSONResponse({"ok": True, "filename": dest.name})
+
+
+@app.delete("/api/activity/{activity_id}/images/{filename}")
+async def delete_image(activity_id: str, filename: str) -> JSONResponse:
+    dd = _get_data_dir()
+    target = dd / "edits" / "images" / activity_id / filename
+    if target.exists() and target.is_file():
+        target.unlink()
+        # Remove empty parent dir
+        if not any(target.parent.iterdir()):
+            shutil.rmtree(target.parent)
+    return JSONResponse({"ok": True})

bincio/render/cli.py

@@ -61,11 +61,23 @@ def _ensure_npm(site: Path) -> None:
         subprocess.run(["npm", "install"], cwd=site, check=True)
 
 
+def _merge_edits(data: Path) -> None:
+    """Run the sidecar merge step, producing data/_merged/."""
+    from bincio.render.merge import merge_all
+    n = merge_all(data)
+    if n:
+        console.print(f"Merged [cyan]{n}[/cyan] sidecar edit(s) into _merged/")
+    else:
+        console.print("No sidecars found — _merged/ mirrors extracted data.")
+
+
 def _link_data(site: Path, data: Path) -> None:
-    """Symlink the BAS data store into site/public/data."""
+    """Symlink site/public/data → data/_merged/ (the post-merge output)."""
+    merged = data / "_merged"
+    target = merged if merged.exists() else data
     public_data = site / "public" / "data"
     if public_data.is_symlink():
-        if public_data.resolve() == data:
+        if public_data.resolve() == target.resolve():
             return  # already correct
         public_data.unlink()
     elif public_data.exists():
@@ -74,8 +86,8 @@ def _link_data(site: Path, data: Path) -> None:
             "remove it manually if you want bincio to manage it."
         )
         return
-    public_data.symlink_to(data)
-    console.print(f"Linked data: [cyan]{data}[/cyan] → [cyan]{public_data}[/cyan]")
+    public_data.symlink_to(target)
+    console.print(f"Linked data: [cyan]{target}[/cyan] → [cyan]{public_data}[/cyan]")
 
 
 @click.command()
@@ -108,6 +120,7 @@ def render(
     console.print(f"Data:  [cyan]{data}[/cyan]")
 
     _ensure_npm(site)
+    _merge_edits(data)
     _link_data(site, data)
 
     env = {**os.environ, "BINCIO_DATA_DIR": str(data)}

bincio/render/merge.py

@@ -0,0 +1,150 @@
+"""Apply sidecar .md edits to BAS JSON files.
+
+Produces data_dir/_merged/ — a mirror of data_dir where:
+- Files without sidecars are symlinked to the originals (cheap, preserves extracted data)
+- Files with sidecars are written as merged copies
+- index.json is rewritten with private filtering + highlight sort
+
+This keeps data_dir/activities/*.json pristine (re-running extract never clobbers
+user edits, and removing a sidecar always reverts fully on the next render).
+"""
+
+from __future__ import annotations
+
+import json
+import re
+import shutil
+from pathlib import Path
+
+import yaml
+
+
+def parse_sidecar(path: Path) -> tuple[dict, str]:
+    """Return (frontmatter_dict, markdown_body) from a sidecar .md file."""
+    text = path.read_text(encoding="utf-8")
+    if text.startswith("---"):
+        parts = re.split(r"^---[ \t]*$", text, maxsplit=2, flags=re.MULTILINE)
+        if len(parts) >= 3:
+            fm = yaml.safe_load(parts[1]) or {}
+            return fm, parts[2].strip()
+    return {}, text.strip()
+
+
+def apply_sidecar(detail: dict, fm: dict, body: str) -> dict:
+    """Apply sidecar overrides to a detail JSON dict. Returns a modified copy."""
+    d = dict(detail)
+    d.setdefault("custom", {})
+    d["custom"] = dict(d["custom"])  # don't mutate original
+
+    if "title" in fm:
+        d["title"] = str(fm["title"])
+    if "sport" in fm:
+        d["sport"] = str(fm["sport"])
+    if "gear" in fm:
+        d["gear"] = str(fm["gear"]) if fm["gear"] else d.get("gear")
+    if body:
+        d["description"] = body
+    elif "description" in fm:
+        d["description"] = str(fm["description"])
+    if "highlight" in fm:
+        d["custom"]["highlight"] = bool(fm["highlight"])
+    if "private" in fm:
+        d["privacy"] = "private" if fm["private"] else detail.get("privacy", "public")
+    if "hide_stats" in fm:
+        d["custom"]["hide_stats"] = [str(s) for s in (fm["hide_stats"] or [])]
+
+    return d
+
+
+def _apply_sidecar_summary(summary: dict, fm: dict) -> dict:
+    """Apply sidecar overrides to an index summary entry."""
+    s = dict(summary)
+    s.setdefault("custom", {})
+    s["custom"] = dict(s["custom"])
+
+    if "title" in fm:
+        s["title"] = str(fm["title"])
+    if "sport" in fm:
+        s["sport"] = str(fm["sport"])
+    if "highlight" in fm:
+        s["custom"]["highlight"] = bool(fm["highlight"])
+    if "private" in fm:
+        s["privacy"] = "private" if fm["private"] else summary.get("privacy", "public")
+
+    return s
+
+
+def merge_all(data_dir: Path) -> int:
+    """Build data_dir/_merged/ with all sidecar overrides applied.
+
+    Returns the number of sidecars found and applied.
+    """
+    edits_dir = data_dir / "edits"
+    acts_dir = data_dir / "activities"
+    merged_dir = data_dir / "_merged"
+    merged_acts = merged_dir / "activities"
+
+    # Collect sidecars upfront
+    sidecars: dict[str, tuple[dict, str]] = {}
+    if edits_dir.exists():
+        for md_path in sorted(edits_dir.glob("*.md")):
+            sidecars[md_path.stem] = parse_sidecar(md_path)
+
+    # Wipe and recreate _merged/activities/
+    if merged_acts.exists():
+        shutil.rmtree(merged_acts)
+    merged_acts.mkdir(parents=True)
+
+    # Mirror activities/ — symlink unmodified, write merged copies for overridden
+    if acts_dir.exists():
+        for src in sorted(acts_dir.iterdir()):
+            if not src.is_file():
+                continue
+            dest = merged_acts / src.name
+            activity_id = src.stem
+            if src.suffix == ".json" and activity_id in sidecars:
+                fm, body = sidecars[activity_id]
+                detail = json.loads(src.read_text(encoding="utf-8"))
+                merged = apply_sidecar(detail, fm, body)
+                dest.write_text(json.dumps(merged, indent=2, ensure_ascii=False))
+            else:
+                dest.symlink_to(src.resolve())
+
+    # Mirror edits/images/ → _merged/activities/images/ so the site can serve them
+    edits_images = edits_dir / "images" if edits_dir.exists() else None
+    if edits_images and edits_images.exists():
+        merged_images = merged_acts / "images"
+        merged_images.mkdir(exist_ok=True)
+        for img_dir in edits_images.iterdir():
+            if img_dir.is_dir():
+                dest_img = merged_images / img_dir.name
+                if not dest_img.exists():
+                    dest_img.symlink_to(img_dir.resolve())
+
+    # Write merged index.json (private filtered, highlight sorted)
+    index_path = data_dir / "index.json"
+    if index_path.exists():
+        index = json.loads(index_path.read_text(encoding="utf-8"))
+        activities = []
+        for s in index.get("activities", []):
+            aid = s.get("id", "")
+            if aid in sidecars:
+                fm, _ = sidecars[aid]
+                s = _apply_sidecar_summary(s, fm)
+            activities.append(s)
+
+        # Drop private activities from the published feed
+        activities = [a for a in activities if a.get("privacy") != "private"]
+
+        # Sort: newest first, then bring highlighted activities to the top
+        activities.sort(key=lambda a: a.get("started_at", ""), reverse=True)
+        activities.sort(key=lambda a: 0 if a.get("custom", {}).get("highlight") else 1)
+
+        index["activities"] = activities
+        (merged_dir / "index.json").write_text(
+            json.dumps(index, indent=2, ensure_ascii=False)
+        )
+    elif (merged_dir / "index.json").exists():
+        (merged_dir / "index.json").unlink()
+
+    return len(sidecars)