chore(examples): PR-review fixes for 05/07/09

- 09 tool-use: handle ``ToolCall.arguments is None`` (provider-
  reported parse error path) and wrap dispatch in a try/except that
  catches KeyError/ValueError/TypeError from bad args. Errors surface
  as ToolMessage content so the model can retry or give up gracefully
  rather than crashing the graph.
- 07 multimodal-prompt: add ``prompts_fallback/production/
  identify-mission.j2`` so the fallback backend actually covers both
  prompts. Without it, a primary outage would let the caption call
  fall through but break the identify call with PromptNotFound.
  Update the in-code comment that previously said fallback shipped
  only one prompt.
- 05 fan-out-with-retry: fix BatchState docstring that referenced
  ``branch_errors`` (the parallel-branches-side name) — the actual
  field is ``instance_errors``.

Author: chris-colinsky

examples/05-fan-out-with-retry/main.py

@@ -127,7 +127,7 @@ async def _chat(system: str, user: str) -> str:
 
 class BatchState(State):
     """Outer graph: list of headlines goes in, parallel lists of summaries
-    and topic tags come out. ``branch_errors`` only populates under
+    and topic tags come out. ``instance_errors`` only populates under
     ``error_policy="collect"`` — each failed instance contributes one
     record naming its ``fan_out_index`` and the exception category."""
 

examples/07-multimodal-prompt/main.py

@@ -129,11 +129,12 @@ def _get_provider() -> OpenAIProvider:
 # Two backends are wired here:
 #   - primary: ``prompts/`` — ships caption-lunar-image and
 #     identify-mission.
-#   - fallback: ``prompts_fallback/`` — ships a backup
-#     caption-lunar-image only. The fallback path fires when the
-#     primary raises ``PromptStoreUnavailable`` (e.g., a remote
-#     primary like Langfuse times out); ``PromptNotFound`` from
-#     primary stops the chain (the name is legitimately missing).
+#   - fallback: ``prompts_fallback/`` — ships shorter variants of
+#     BOTH prompts so the safety net actually covers the whole
+#     pipeline. The fallback path fires when the primary raises
+#     ``PromptStoreUnavailable`` (e.g., a remote primary like
+#     Langfuse times out); ``PromptNotFound`` from primary stops the
+#     chain (the name is legitimately missing).
 #
 # In this demo both prompts live in primary, so the fallback path
 # isn't exercised at runtime. The construction-time setup is the

examples/07-multimodal-prompt/prompts_fallback/production/identify-mission.j2

@@ -0,0 +1,15 @@
+You are looking at a photograph from a lunar mission. The caption
+hint below was written by another system.
+
+Caption hint: {{ caption }}
+
+In ONE short line, name the specific mission shown:
+
+  Mission: <name>
+
+No preamble.
+
+(This is the fallback variant. The primary backend ships the
+canonical identify-mission prompt and is always tried first; this
+file exists so a primary-backend outage doesn't break the demo
+pipeline.)

examples/09-tool-use/main.py

@@ -289,7 +289,20 @@ async def dispatch_tools(s: AgentState) -> Mapping[str, Any]:
         raise RuntimeError("dispatch_tools entered without a tool-calling assistant message")
     tool_messages: list[Message] = []
     for tc in last.tool_calls:
-        result_text = dispatch(tc.name, tc.arguments or {})
+        # ToolCall.arguments is None only under provider-reported
+        # finish_reason="error" (unparseable args). In a real agent the
+        # model sees the error string and either retries or bails;
+        # either way the loop doesn't crash.
+        if tc.arguments is None:
+            result_text = (
+                f"Tool {tc.name!r} could not be invoked: arguments were "
+                f"unparseable. Retry with valid JSON arguments."
+            )
+        else:
+            try:
+                result_text = dispatch(tc.name, tc.arguments)
+            except (KeyError, ValueError, TypeError) as exc:
+                result_text = f"Tool {tc.name!r} failed with {type(exc).__name__}: {exc}"
         tool_messages.append(ToolMessage(content=result_text, tool_call_id=tc.id))
     return {
         "messages": [*s.messages, *tool_messages],