Browse catalog dialog (issue #10 phase 2)

Adds the user-facing half of the server catalog: a searchable, signed
catalog browser wired to the existing paste/import path.

bcc_core.py (pure, GUI-free, per the design comment on #10):
- CATALOG_CATEGORY_GROUPS / catalog_category_group(): collapses the
  raw taxonomy to the 7 UI chips (unknown categories fall back to
  Other, never drop an entry).
- catalog_entry_matches_query() / filter_catalog_entries() /
  catalog_entries_in_group(): search-as-you-type + category chip
  filtering over catalog entries.
- format_freshness_hint(): last_release ISO date -> "Last updated N
  months/years ago", '' when missing/unparseable/future.
- first_unfilled_focus_target(): finds the first <PLACEHOLDER> arg or
  blank env_required key so the GUI can focus it after Add.
- load_bundled_catalog_entries(): reads+verifies+validates the
  bundled catalog.json/.sig pair, returns servers or an EMPTY list on
  ANY failure -- the load-bearing guarantee behind the dialog's empty
  state.
- Bug fix: catalog_entry_to_paste_json() only copied config.env,
  ignoring env_required -- the field where 9 of the 19 seed entries
  (postgres, github, notion, obsidian, brave-search, tavily,
  home-assistant, n8n, grafana) actually declare their secret var
  names. Add would have silently added these servers with no env
  field for the user to fill in. Now env_required keys are seeded as
  empty-string placeholders unless config.env already sets them.

bcc.py:
- BrowseCatalogDialog: search box, category chips, list, detail pane
  (description/notes/homepage/freshness hint/verbatim command
  preview), per-tier action (Add for basic, Open setup docs for
  link-only). Every catalog-derived string goes through plain_label()
  (Qt.PlainText + html.escape, matching catalog_console.py's
  approach) or an inherently-plain QPlainTextEdit for the command
  preview -- catalog.json takes community PRs, so every field is
  attacker-influenceable.
- "Browse catalog…" button next to Paste JSON.
- ServerEditor.focus_target(): selects the first unfilled arg line or
  opens the env-table cell editor for the first blank env row.
- Save-time placeholder guard: warns (Yes/No, defaults No) when any
  server still has an unfilled <PLACEHOLDER>; never blocks a
  deliberate save, never saves one unnoticed.

bcc.spec: bundle data/catalog.json.sig alongside catalog.json -- the
signature file was missing from datas, so a frozen build would have
had a catalog.json with no matching .sig for resolve_catalog() to
verify against.

tests/test_core.py: +82 tests covering category-group mapping,
catalog search/filter, freshness-hint formatting (including the
month/year rounding boundary), first_unfilled_focus_target, the
catalog_entry_to_paste_json env_required fix (incl. a regression
against the real shipped postgres entry), and
load_bundled_catalog_entries under valid/tampered/wrong-key/missing-
file/invalid-but-signed conditions plus an end-to-end check against
the real data/catalog.json + .sig (19 entries).

GUI code (BrowseCatalogDialog, ServerEditor.focus_target,
MainWindow.browse_catalog) is unavoidably untested here -- PySide6
cannot import in this sandbox (missing libEGL/system GL libs) -- but
all the logic it depends on is pushed into bcc_core.py and covered
above.

bcc.py

@@ -10,6 +10,7 @@ Run:  python mcp_manager.py
 
 from __future__ import annotations
 
+import html
 import sys
 import time
 from pathlib import Path
@@ -26,10 +27,12 @@ from PySide6.QtGui import (
     QKeySequence,
     QPainter,
     QPixmap,
+    QTextCursor,
 )
 from PySide6.QtWidgets import (
     QAbstractItemView,
     QApplication,
+    QButtonGroup,
     QCheckBox,
     QComboBox,
     QDialog,
@@ -65,6 +68,26 @@ import bcc_core as core
 # thread during drag-and-drop import, so skip anything larger than this.
 MAX_DROP_IMPORT_BYTES = 5 * 1024 * 1024  # 5 MB
 
+
+def plain_label(text: object) -> QLabel:
+    """A QLabel guaranteed to render `text` as plain text, never HTML.
+
+    Qt's QLabel auto-interprets HTML by default (Qt.AutoText). Every catalog
+    entry field (description, notes, display name, urls -- and especially
+    args) is attacker-influenceable: catalog.json accepts community PRs, and
+    only a valid Ed25519 signature stands between a PR and what a user sees
+    here. A `<b>` or `<img onerror=...>` in a description must render as
+    visible text, not markup -- exactly the same reasoning catalog_console.py
+    documents for its own plain_label(). Every catalog-derived string shown
+    by the Browse dialog MUST go through this helper (or an inherently
+    plain-text widget like QPlainTextEdit) rather than a bare QLabel(...).
+    """
+    label = QLabel(html.escape(str(text)))
+    label.setTextFormat(Qt.TextFormat.PlainText)
+    label.setWordWrap(True)
+    return label
+
+
 # --- One-line rebrand: change this to recolor the whole app --------------- #
 ACCENT = "#f97316"  # warm orange
 ACCENT_DIM = "#c2570b"
@@ -676,6 +699,39 @@ class ServerEditor(QFrame):
     def current_name(self) -> str:
         return self.name.text().strip()
 
+    def focus_target(self, target: tuple[str, int | str] | None):
+        """
+        Focus the field a catalog Add left unfilled -- `target` is whatever
+        core.first_unfilled_focus_target() returned: ("args", line_index),
+        ("env", var_name), or None (nothing to fill, so do nothing).
+
+        Only meaningful on the stdio page, which is the only page a catalog
+        entry ever populates (link-only entries never reach dump_data()).
+        """
+        if not target or self.type.currentIndex() != 0:
+            return
+        kind, value = target
+        if kind == "args":
+            self.args.setFocus()
+            cursor = self.args.textCursor()
+            cursor.movePosition(QTextCursor.MoveOperation.Start)
+            cursor.movePosition(
+                QTextCursor.MoveOperation.Down, QTextCursor.MoveMode.MoveAnchor, int(value)
+            )
+            cursor.movePosition(
+                QTextCursor.MoveOperation.EndOfLine, QTextCursor.MoveMode.KeepAnchor
+            )
+            self.args.setTextCursor(cursor)
+        elif kind == "env":
+            for r in range(self.env.table.rowCount()):
+                key_item = self.env.table.item(r, 0)
+                if key_item and key_item.text() == value:
+                    self.env.table.setCurrentCell(r, 1)
+                    val_item = self.env.table.item(r, 1)
+                    if val_item:
+                        self.env.table.editItem(val_item)
+                    break
+
     def _type_switched(self):
         self.stack.setCurrentIndex(self.type.currentIndex())
         self._emit()
@@ -1204,6 +1260,262 @@ class PasteDialog(QDialog):
             self.err.setText(str(e))
 
 
+# --------------------------------------------------------------------------- #
+# Browse catalog dialog (issue #10 phase 2): search/filter the signed,
+# bundled server catalog and add a "basic" entry through the existing
+# paste/import path, or send a "link-only" entry to its setup docs.
+#
+# Every widget here that shows catalog-derived text uses plain_label() or an
+# inherently-plain widget (QPlainTextEdit) -- see plain_label()'s docstring.
+# The dialog itself does no signature/schema work: MainWindow hands it an
+# already-verified `entries` list (bcc_core.load_bundled_catalog_entries()),
+# and an empty list here means "show the empty state", never "fall back to
+# something less trusted".
+# --------------------------------------------------------------------------- #
+class BrowseCatalogDialog(QDialog):
+    def __init__(self, parent, entries: list[dict]):
+        super().__init__(parent)
+        self.setWindowTitle("Browse catalog")
+        self.resize(880, 560)
+        self.entries = entries or []
+        self.result_entry: dict | None = None
+        self._current_entry: dict | None = None
+        self._current_homepage: str | None = None
+        self._current_docs_url: str | None = None
+        self._current_group = "All"
+
+        outer = QVBoxLayout(self)
+
+        if not self.entries:
+            # Signature verification failed, or nothing was bundled -- never
+            # show a half-trusted list, and never explain WHY beyond this;
+            # a stale/tampered catalog isn't the user's problem to diagnose.
+            msg = plain_label("Catalog unavailable.")
+            msg.setObjectName("placeholder")
+            msg.setAlignment(Qt.AlignmentFlag.AlignCenter)
+            outer.addWidget(msg, 1)
+            btns = QDialogButtonBox(QDialogButtonBox.StandardButton.Close)
+            btns.rejected.connect(self.reject)
+            outer.addWidget(btns)
+            return
+
+        search_row = QHBoxLayout()
+        self.search_box = QLineEdit()
+        self.search_box.setPlaceholderText("Search by name, description, or category…")
+        self.search_box.setClearButtonEnabled(True)
+        self.search_box.textChanged.connect(self._refresh_list)
+        search_row.addWidget(self.search_box, 1)
+        outer.addLayout(search_row)
+
+        chip_row = QHBoxLayout()
+        self._chip_group = QButtonGroup(self)
+        self._chip_group.setExclusive(True)
+        for label in core.CATALOG_CATEGORY_CHIPS:
+            btn = QPushButton(label)
+            btn.setCheckable(True)
+            btn.setChecked(label == "All")
+            btn.clicked.connect(lambda _checked=False, g=label: self._set_group(g))
+            self._chip_group.addButton(btn)
+            chip_row.addWidget(btn)
+        chip_row.addStretch()
+        outer.addLayout(chip_row)
+
+        splitter = QSplitter(Qt.Orientation.Horizontal)
+
+        left = QWidget()
+        lv = QVBoxLayout(left)
+        lv.setContentsMargins(0, 0, 0, 0)
+        self.list = QListWidget()
+        self.list.currentItemChanged.connect(self._on_selected)
+        lv.addWidget(self.list, 1)
+        splitter.addWidget(left)
+
+        right = QFrame()
+        right.setObjectName("card")
+        rv = QVBoxLayout(right)
+        self.detail_title = plain_label("")
+        self.detail_title.setObjectName("h1")
+        rv.addWidget(self.detail_title)
+        self.detail_meta = plain_label("")
+        self.detail_meta.setObjectName("muted")
+        rv.addWidget(self.detail_meta)
+        self.detail_freshness = plain_label("")
+        self.detail_freshness.setObjectName("muted")
+        rv.addWidget(self.detail_freshness)
+        self.detail_desc = plain_label("")
+        rv.addWidget(self.detail_desc)
+        self.detail_notes = plain_label("")
+        self.detail_notes.setObjectName("muted")
+        rv.addWidget(self.detail_notes)
+        self.detail_homepage_btn = QPushButton("Open homepage")
+        self.detail_homepage_btn.clicked.connect(self._open_homepage)
+        rv.addWidget(self.detail_homepage_btn)
+        rv.addWidget(plain_label("Exact command this will add:"))
+        self.detail_command_preview = QPlainTextEdit()
+        self.detail_command_preview.setObjectName("diag")
+        self.detail_command_preview.setReadOnly(True)
+        # Read-only QPlainTextEdit never interprets HTML, regardless of what
+        # a compromised/careless catalog entry's command/args contain -- this
+        # is the field that renders "the exact bytes that will be written".
+        rv.addWidget(self.detail_command_preview, 1)
+        self.detail_action_btn = QPushButton("")
+        self.detail_action_btn.setObjectName("primary")
+        self.detail_action_btn.clicked.connect(self._on_action)
+        rv.addWidget(self.detail_action_btn)
+        splitter.addWidget(right)
+
+        splitter.setSizes([360, 480])
+        outer.addWidget(splitter, 1)
+
+        btns = QDialogButtonBox(QDialogButtonBox.StandardButton.Close)
+        btns.rejected.connect(self.reject)
+        outer.addWidget(btns)
+
+        self._refresh_list()
+
+    # --- list / filtering -------------------------------------------------- #
+    def _set_group(self, group: str):
+        self._current_group = group
+        self._refresh_list()
+
+    def _visible_entries(self) -> list[dict]:
+        filtered = core.filter_catalog_entries(self.entries, self.search_box.text())
+        return core.catalog_entries_in_group(filtered, self._current_group)
+
+    def _format_row(self, entry: dict) -> str:
+        display = str(entry.get("display") or entry.get("id") or "")
+        official = "✓ " if entry.get("official") else ""
+        stars = entry.get("stars")
+        star_txt = f"   ★ {stars:,}" if isinstance(stars, int) else ""
+        group = core.catalog_category_group(entry.get("category", ""))
+        desc = str(entry.get("description") or "")
+        if len(desc) > 88:
+            desc = desc[:87] + "…"
+        # QListWidgetItem text is always rendered literally by Qt (no HTML
+        # interpretation), so no escaping is needed here -- unlike QLabel.
+        return f"{official}{display}{star_txt}\n{desc}   ·   {group}"
+
+    def _refresh_list(self):
+        self.list.blockSignals(True)
+        self.list.clear()
+        for entry in self._visible_entries():
+            item = QListWidgetItem(self._format_row(entry))
+            item.setData(Qt.ItemDataRole.UserRole, entry)
+            # Tooltips DO auto-detect rich text in Qt, so escape defensively
+            # even though descriptions are already shown, unescaped-but-safe,
+            # in the QListWidgetItem text above.
+            item.setToolTip(html.escape(str(entry.get("description", ""))))
+            self.list.addItem(item)
+        self.list.blockSignals(False)
+        if self.list.count():
+            self.list.setCurrentRow(0)
+        else:
+            self._on_selected(None, None)
+
+    # --- detail pane -------------------------------------------------------- #
+    def _on_selected(self, current, _previous=None):
+        if current is None:
+            self._current_entry = None
+            self._current_homepage = None
+            self._current_docs_url = None
+            self.detail_title.setText("")
+            self.detail_meta.setText("")
+            self.detail_freshness.setText("")
+            self.detail_desc.setText("No matching servers." if self.entries else "")
+            self.detail_notes.setText("")
+            self.detail_homepage_btn.setVisible(False)
+            self.detail_command_preview.setPlainText("")
+            self.detail_action_btn.setEnabled(False)
+            self.detail_action_btn.setText("Add")
+            return
+
+        entry = current.data(Qt.ItemDataRole.UserRole)
+        self._current_entry = entry
+        self.detail_title.setText(str(entry.get("display") or entry.get("id") or ""))
+
+        official = "✓ Official" if entry.get("official") else ""
+        stars = entry.get("stars")
+        star_txt = f"★ {stars:,}" if isinstance(stars, int) else ""
+        group = core.catalog_category_group(entry.get("category", ""))
+        meta_bits = [b for b in (official, star_txt, group) if b]
+        self.detail_meta.setText("  ·  ".join(meta_bits))
+
+        freshness = core.format_freshness_hint(entry.get("last_release"))
+        self.detail_freshness.setText(freshness)
+        self.detail_freshness.setVisible(bool(freshness))
+
+        self.detail_desc.setText(str(entry.get("description") or ""))
+
+        notes = entry.get("notes") or ""
+        self.detail_notes.setText(notes)
+        self.detail_notes.setVisible(bool(notes))
+
+        homepage = entry.get("homepage")
+        self._current_homepage = homepage if isinstance(homepage, str) else None
+        self.detail_homepage_btn.setVisible(bool(self._current_homepage))
+
+        self._current_docs_url = (
+            entry.get("docs_url") if isinstance(entry.get("docs_url"), str) else None
+        )
+
+        self.detail_command_preview.setPlainText(self._render_command_preview(entry))
+
+        if entry.get("setup") == "basic":
+            self.detail_action_btn.setText("Add")
+            self.detail_action_btn.setEnabled(True)
+        else:
+            self.detail_action_btn.setText("Open setup docs")
+            self.detail_action_btn.setEnabled(bool(self._current_docs_url))
+
+    def _render_command_preview(self, entry: dict) -> str:
+        """
+        The exact command that will be written, rendered verbatim. Every
+        value here comes straight from the (signature-verified) catalog
+        entry with no interpretation beyond str() -- this must never be the
+        place a markup-laced description sneaks back in as "helpful"
+        formatting.
+        """
+        if entry.get("setup") != "basic":
+            docs = entry.get("docs_url") or "(none provided)"
+            return (
+                "This is a hosted/managed integration -- there is no local "
+                "command to add.\n\nSetup docs:\n  " + str(docs)
+            )
+
+        config = entry.get("config") or {}
+        lines = [f"command: {config.get('command', '')}"]
+        args = config.get("args") or []
+        if args:
+            lines.append("args:")
+            lines.extend(f"  {a}" for a in args)
+        env = config.get("env") or {}
+        env_required = entry.get("env_required") or {}
+        env_keys = list(env.keys()) + [k for k in env_required if k not in env]
+        if env_keys:
+            lines.append("env (names only -- you provide the values):")
+            lines.extend(f"  {k}" for k in env_keys)
+        return "\n".join(lines)
+
+    def _open_homepage(self):
+        url = self._current_homepage
+        if url and url.startswith("https://"):
+            QDesktopServices.openUrl(QUrl(url))
+
+    def _on_action(self):
+        entry = self._current_entry
+        if not entry:
+            return
+        if entry.get("setup") == "basic":
+            self.result_entry = entry
+            self.accept()
+        else:
+            url = self._current_docs_url
+            if url and url.startswith("https://"):
+                QDesktopServices.openUrl(QUrl(url))
+            # link-only never auto-adds and never closes the dialog -- the
+            # user can keep browsing after opening the docs in their browser.
+
+
 # --------------------------------------------------------------------------- #
 # Log viewer dialog (issue #6): a read-only, auto-tailing view of a single
 # server's MCP log file. Polls on a QTimer instead of watching the filesystem
@@ -1780,6 +2092,10 @@ class MainWindow(QMainWindow):
         self.del_btn = QPushButton("Delete")
         self.del_btn.setObjectName("danger")
         self.paste_btn = QPushButton("Paste JSON...")
+        self.browse_catalog_btn = QPushButton("Browse catalog…")
+        self.browse_catalog_btn.setToolTip(
+            "Add a popular MCP server from the curated, signed catalog"
+        )
         self.copy_btn = QPushButton("Copy to ▸")
         self.undo_btn = QPushButton("Undo")
         self.undo_btn.setEnabled(False)
@@ -1792,6 +2108,7 @@ class MainWindow(QMainWindow):
         self.dup_btn.clicked.connect(self.duplicate_server)
         self.del_btn.clicked.connect(self.delete_server)
         self.paste_btn.clicked.connect(self.paste_json)
+        self.browse_catalog_btn.clicked.connect(self.browse_catalog)
         self.copy_btn.clicked.connect(self.copy_to_menu)
         self.undo_btn.clicked.connect(self._undo)
         self.test_all_btn.clicked.connect(self._test_all_servers)
@@ -1800,6 +2117,7 @@ class MainWindow(QMainWindow):
             self.dup_btn,
             self.del_btn,
             self.paste_btn,
+            self.browse_catalog_btn,
             self.copy_btn,
             self.undo_btn,
             self.test_all_btn,
@@ -2378,6 +2696,41 @@ class MainWindow(QMainWindow):
         self._mark_dirty()
         self.status.setText(f"Imported {added} added, {replaced} replaced. Review and Save.")
 
+    def browse_catalog(self):
+        """
+        Open the Browse-catalog dialog (issue #10 phase 2). The catalog is
+        loaded and signature-verified fresh every time the dialog opens --
+        never cached across app runs at this phase (remote fetch/cache is
+        #61, not yet built) -- so a bundled-catalog swap only takes effect
+        on next dialog open, never mid-session in a stale way.
+        """
+        entries = core.load_bundled_catalog_entries(
+            _asset_dir() / "data" / "catalog.json", _asset_dir() / "data" / "catalog.json.sig"
+        )
+        dlg = BrowseCatalogDialog(self, entries)
+        if dlg.exec() != QDialog.DialogCode.Accepted or not dlg.result_entry:
+            return
+        entry = dlg.result_entry
+        paste = core.catalog_entry_to_paste_json(entry)
+        name, data = next(iter(paste.items()))
+
+        existing_before = {s.name: i for i, s in enumerate(self.servers)}
+        self._push_undo()
+        _added, replaced = self._import_server(name, data)
+        idx = (
+            existing_before.get(name, len(self.servers) - 1) if replaced else len(self.servers) - 1
+        )
+        self._refresh_tables(select_index=idx)
+        self._mark_dirty()
+
+        target = core.first_unfilled_focus_target(data)
+        self.editor.focus_target(target)
+
+        verb = "Replaced" if replaced else "Added"
+        self.status.setText(
+            f"{verb} “{name}” from the catalog. Fill in the highlighted field and Save."
+        )
+
     def copy_to_menu(self):
         idx = self._current_index()
         if not (0 <= idx < len(self.servers)):
@@ -2456,6 +2809,29 @@ class MainWindow(QMainWindow):
             QMessageBox.warning(self, "Can't save yet", "Fix the highlighted problem first.")
             return
 
+        # Placeholder guard (issue #10): a catalog Add can leave a
+        # <PLACEHOLDER>-style token in args/env until the user fills it in.
+        # This warns, it does not block -- the user may be deliberately
+        # saving a stub to finish later -- but it must never save silently,
+        # since a server launched with a literal "<PLACEHOLDER>" argument
+        # just fails in a confusing way at spawn time.
+        placeholder_names = [
+            s.name for s in self.servers if core.config_has_unfilled_placeholders(s.data)
+        ]
+        if placeholder_names:
+            names = ", ".join(f"“{n}”" for n in placeholder_names)
+            ans = QMessageBox.warning(
+                self,
+                "Unfilled placeholder",
+                f"{names} still has a <PLACEHOLDER> value that hasn't been "
+                "replaced with a real value. Claude won't be able to use "
+                "it as-is.\n\nSave anyway?",
+                QMessageBox.StandardButton.Yes | QMessageBox.StandardButton.No,
+                QMessageBox.StandardButton.No,
+            )
+            if ans != QMessageBox.StandardButton.Yes:
+                return
+
         # Stale-file check: if the file changed on disk since we loaded it, prompt.
         # Compare mtime AND size (not mtime alone) so a concurrent external write
         # that lands within the mtime resolution window, or that restores the