fix(acp): also mark raised-exception tool results as failed

Extends #26573 to also catch the case the original PR deliberately left
out: when a tool raises an exception, the agent's tool executor wraps it
in a canonical 'Error executing tool '<name>': ...' string prefix (see
agent/tool_executor.py around the try/except). That prefix is unique to
the wrapper and cannot legitimately appear in well-behaved tool output,
so it is a safe signal that the tool blew up.

Without this, the canonical 'tool raised' case still rendered as a green
'completed' row in Zed despite being a runtime failure — exactly the
class of bug #26573 set out to fix.

Adds a positive test (raised-exception prefix -> failed) and a negative
test (bare 'Error:' word in legit tool output stays completed) so a
future contributor doesn't accidentally widen the rule to false-positive
on compiler/linter diagnostics.

acp_adapter/tools.py

@@ -209,6 +209,15 @@ def _tool_result_failed(result: Optional[str], tool_name: str | None = None) ->
     "error" because tests failed or a command printed diagnostics; Zed should
     only receive ACP failed status for structured tool-level failures.
     """
+    # Raised exceptions from the agent's tool executor get wrapped in a
+    # canonical "Error executing tool '<name>': ..." prefix (see
+    # agent/tool_executor.py around the try/except). That prefix is uniquely
+    # produced by the wrapper itself — it cannot legitimately appear in
+    # well-behaved tool output. Catch it so a tool that blew up shows as
+    # failed in Zed instead of misleadingly green.
+    if isinstance(result, str) and result.startswith("Error executing tool '"):
+        return True
+
     data = _json_loads_maybe(result)
     if not isinstance(data, dict):
         return False

tests/acp/test_tools.py

@@ -365,6 +365,31 @@ class TestBuildToolComplete:
         result = build_tool_complete("tc-ok", "terminal", "tests failed: 1 assertion error")
         assert result.status == "completed"
 
+    def test_build_tool_complete_marks_raised_exception_prefix_as_failed(self):
+        """The agent's tool executor wraps raised exceptions in a canonical
+        "Error executing tool '<name>': ..." prefix. That prefix is unique to
+        the wrapper and means the tool blew up, so it must surface as failed
+        in Zed regardless of whether the body parses as JSON.
+        """
+        result = build_tool_complete(
+            "tc-fail-exc",
+            "patch",
+            "Error executing tool 'patch': KeyError: 'foo'",
+        )
+        assert result.status == "failed"
+
+    def test_build_tool_complete_does_not_match_error_word_alone(self):
+        """Bare 'Error: ...' messages (without the unique 'Error executing
+        tool '<name>':' prefix) must still be reported as completed — they
+        legitimately appear in compiler/linter/test output.
+        """
+        result = build_tool_complete(
+            "tc-ok-error-word",
+            "terminal",
+            "Error: pytest collected 0 items",
+        )
+        assert result.status == "completed"
+
     def test_build_tool_complete_marks_structured_polished_tool_error_as_failed(self):
         result = build_tool_complete("tc-fail", "read_file", '{"error": "File not found"}')
         assert result.status == "failed"