fix(coding-agent): remove process-cwd tool singletons and use tool-name allowlists

- switch SDK/CLI tool selection to name-based allowlists
- apply allowlists across built-in, extension, and SDK tools
- remove ambient process.cwd defaults from core tooling and resource helpers
- update tests, examples, and TUI callers for explicit cwd plumbing
- add regression coverage for extension tool filtering

closes #3452
closes #2835

packages/coding-agent/docs/tui.md

@@ -741,11 +741,16 @@ Customize the inline working indicator shown while pi is streaming a response.
 
 ```typescript
 // Static indicator
-ctx.ui.setWorkingIndicator({ frames: ["●"] });
+ctx.ui.setWorkingIndicator({ frames: [ctx.ui.theme.fg("accent", "●")] });
 
 // Custom animated indicator
 ctx.ui.setWorkingIndicator({
-  frames: ["·", "•", "●", "•"],
+  frames: [
+    ctx.ui.theme.fg("dim", "·"),
+    ctx.ui.theme.fg("muted", "•"),
+    ctx.ui.theme.fg("accent", "●"),
+    ctx.ui.theme.fg("muted", "•"),
+  ],
   intervalMs: 120,
 });
 
@@ -756,7 +761,7 @@ ctx.ui.setWorkingIndicator({ frames: [] });
 ctx.ui.setWorkingIndicator();
 ```
 
-This only affects the normal streaming working indicator. Compaction and retry loaders keep their built-in styling.
+This only affects the normal streaming working indicator. Compaction and retry loaders keep their built-in styling. Custom frames are rendered verbatim, so extensions must add their own colors when needed.
 
 **Examples:** [working-indicator.ts](../examples/extensions/working-indicator.ts)