feat: Add workspace: confine agent tools to a folder (#1103)

* feat: Add workspace: confine agent tools to a folder

Pick a server folder as the agent's workspace so its file/shell tools work
there and don't touch files outside it. File tools are hard-confined; bash/
python run with cwd set to the folder.

Includes a slash command: `/workspace` (alias `/ws`) — show / `set <path>` /
`clear` / `pick` (open the directory browser).

- routes/workspace_routes.py: GET /api/workspace/browse (admin-only).
- src/tool_execution.py: hard path confinement for read_file/write_file;
  bash/python cwd. Threaded route → stream_agent_loop → execute_tool_block.
- src/agent_loop.py: workspace note prepended to the system prompt.
- static/: overflow menu item, input-bar pill, directory-browser modal, and
  the /workspace slash command.
- tests/test_workspace_confine.py.

* Wire workspace confinement into tools that landed after this PR

edit_file (#1239) and grep/glob/ls (#1670) merged after workspace-confine was
written, so they bypassed the workspace boundary. Thread the workspace through:
  - edit_file: _do_edit_file resolves via _resolve_tool_path_in_workspace
  - grep/glob/ls: _resolve_search_root confines to the workspace (root + paths)
  - bash/python/bg cwd: workspace or _AGENT_WORKDIR (keep the #2586 data-dir
    default when no workspace is set)
Tests cover edit_file + grep/ls confinement (inside ok, outside rejected).

* Workspace picker: editable path bar + modal style cohesion + cross-platform hardening

- Make the current-folder strip an editable address bar: type/paste a full
  path and press Enter to navigate (also reaches other Windows drives and
  hidden dirs the up-only browser cannot).
- Reuse shared modal CSS: drop bespoke .workspace-modal-content/.workspace-btn*
  in favour of base .modal-content/.modal-body and the .confirm-btn button
  family; separators/hover use var(--border). Net -31 CSS lines.
- Fix the path field overflowing the modal right edge (flex stretch + margin
  vs an overflow:auto scrollbar-feedback loop): full-bleed, no h-margin.
- Cross-platform confinement: normcase the workspace commonpath check so
  containment holds on case-insensitive filesystems (Windows/macOS).
- Make tests OS-portable: sibling temp dirs instead of /etc, python os.getcwd()
  instead of pwd. 5 pass.

src/agent_loop.py

@@ -1387,6 +1387,7 @@ async def stream_agent_loop(
     owner: Optional[str] = None,
     relevant_tools: Optional[Set[str]] = None,
     fallbacks: Optional[List[tuple]] = None,
+    workspace: Optional[str] = None,
     _is_teacher_run: bool = False,
 ) -> AsyncGenerator[str, None]:
     """Streaming agent loop generator.
@@ -1553,6 +1554,27 @@ async def stream_agent_loop(
         compact=_is_api_model,
         owner=owner,
     )
+    if workspace:
+        # PREPEND (not append) so it dominates the large base prompt — appended
+        # at the end, small models ignored it and asked the user for code. The
+        # folder IS the project; the agent must explore it, not ask.
+        _ws_note = (
+            f"## ACTIVE WORKSPACE — READ FIRST\n"
+            f"The user is working in this folder: {workspace}\n"
+            f"It IS the project. bash/python run with cwd set here and "
+            f"read_file/write_file are confined to it (paths outside are rejected).\n"
+            f"When the user says \"the code\" / \"this project\" / \"the workspace\" "
+            f"or asks to review/find/edit something WITHOUT a path, they mean THIS "
+            f"folder. Do NOT ask the user for code or a path, and do NOT read a file "
+            f"literally named \"workspace\". ALWAYS start by exploring it yourself: "
+            f"run `bash` → `git ls-files` (or `ls -R`) to see the files, then "
+            f"read_file the relevant ones by path RELATIVE to the workspace."
+        )
+        if messages and messages[0].get("role") == "system":
+            messages[0]["content"] = _ws_note + "\n\n" + (messages[0].get("content") or "")
+        else:
+            messages.insert(0, {"role": "system", "content": _ws_note})
+        logger.info("[workspace] active for this turn: %s", workspace)
     prep_timings["prompt_build"] = time.time() - _t2
 
     _t3 = time.time()
@@ -2117,6 +2139,7 @@ async def stream_agent_loop(
                         disabled_tools=disabled_tools,
                         owner=owner,
                         progress_cb=_push_progress,
+                        workspace=workspace,
                     )
                 finally:
                     # Sentinel so the drainer knows to stop.