fix: empty response handling, /no_think model gating, per-model profiles

- Detect empty LLM responses (no content, no tool calls) instead of
  silently treating them as task completion. Retries once without tools
  before warning the user.
- Gate /no_think system message and chat_template_kwargs to Qwen/QwQ
  models only — sending /no_think to llama3.x caused empty responses.
- Add model_profiles config section for per-model overrides (token
  budget, thinking, temperature, max_tokens) matched by name prefix.
  Applied at startup and on /model switch.
- Update SessionManager on /model switch so session files record the
  correct model.
- Add NDJSON fallback in SSE stream parser for Ollama compatibility.
- Improve read_file error to suggest find_files on FileNotFoundError.
- Add diagnostic logging for empty streams and empty results.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/ui/app.py

@@ -75,6 +75,9 @@ class SneakyCodeApp(App):
         """Initialize agent components after the app is mounted."""
         setup_logging_for_tui()
 
+        # Apply model profile for the initial model before creating context
+        self._config.apply_model_profile(self._config.llm.model)
+
         self._ctx = SessionContext(self._config)
 
         # Create long-lived agent dependencies (reused across turns)
@@ -255,8 +258,29 @@ class SneakyCodeApp(App):
             else:
                 new_model = parts[1].strip()
                 self._config.llm.model = new_model
+                if self._session_mgr:
+                    self._session_mgr.update_model(new_model)
+                # Apply model-specific profile overrides
+                profile = self._config.apply_model_profile(new_model)
+                if profile and self._ctx:
+                    # Update token budget if the profile overrides it
+                    self._ctx.token_counter.budget = self._config.agent.max_conversation_tokens
                 self.query_one(HeaderPanel).update_model(new_model)
-                log.write(Text(f"Switched to model: {new_model}", style="bold green"))
+                header = self.query_one(HeaderPanel)
+                header.update_tokens(
+                    self._ctx.estimated_tokens if self._ctx else 0,
+                    self._config.agent.max_conversation_tokens,
+                )
+                msg = f"Switched to model: {new_model}"
+                if profile:
+                    overrides = []
+                    if profile.max_conversation_tokens is not None:
+                        overrides.append(f"tokens={profile.max_conversation_tokens:,}")
+                    if profile.thinking is not None:
+                        overrides.append(f"thinking={'on' if profile.thinking else 'off'}")
+                    if overrides:
+                        msg += f" ({', '.join(overrides)})"
+                log.write(Text(msg, style="bold green"))
         elif cmd.split()[0] == "/mode":
             parts = command.split(maxsplit=1)
             if len(parts) == 1: