sse_emitter: log sanitized single-line tool_buffer on parse failure (Stage 3)

[dpavlin]

Refs #644 (Stage 3 of 3, builds upon Stage 2)

Description

This PR improves observability and diagnostic logging for streaming tool call parse failures:

• When tool parsing fails on an intercepted tool buffer, SseEmitter::emit_finish logs the raw intercepted buffer.
• To prevent multiline splitting and corruption in line-oriented log aggregators (e.g. journalctl), the payload is escaped via escape_for_logging:
  • Standard escape sequences (\n, \r, \t, \\, \', \0).
  • Non-printable control characters escaped using fixed-width 4-digit \u00%02x (avoiding variable-width hex ambiguity when followed by literal hex characters).

Verification

• Added test_escape_for_logging unit test covering NUL bytes, standard escapes, and control characters followed by hex digits.
• Added test_emitter_suppresses_malformed_multiline_tool_buffer asserting that the full escaped payload appears on a single stderr line.
• All 402 unit tests passing (100%).

[cubic-dev-ai]

1 issue found across 6 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="server/src/server/tool_parser.cpp">

<violation number="1" location="server/src/server/tool_parser.cpp:585">
P2: Malformed `arguments`/`parameters` strings are now accepted instead of rejected. Previously `json::parse(...)` in a try/catch returned `false`, dropping the call; now `parse_arg_string_or_obj` returns `true` with an empty args object while preserving the raw (unparseable) string as `tool_call.arguments`. Because `parse_tool_calls` returns that call, `tool_calls_` is non-empty in `emit_finish`, so the new "parse failed; suppressing buffered tool text" logging never fires for these buffers, and a call whose arguments are not valid JSON is emitted to clients as a valid tool call. Confirm this is the intended Stage-3 behavior; if the goal is only better diagnostics, consider keeping the suppression for unparseable argument strings.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

P2: Malformed arguments/parameters strings are now accepted instead of rejected. Previously json::parse(...) in a try/catch returned false, dropping the call; now parse_arg_string_or_obj returns true with an empty args object while preserving the raw (unparseable) string as tool_call.arguments. Because parse_tool_calls returns that call, tool_calls_ is non-empty in emit_finish, so the new "parse failed; suppressing buffered tool text" logging never fires for these buffers, and a call whose arguments are not valid JSON is emitted to clients as a valid tool call. Confirm this is the intended Stage-3 behavior; if the goal is only better diagnostics, consider keeping the suppression for unparseable argument strings.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At server/src/server/tool_parser.cpp, line 585:

<comment>Malformed `arguments`/`parameters` strings are now accepted instead of rejected. Previously `json::parse(...)` in a try/catch returned `false`, dropping the call; now `parse_arg_string_or_obj` returns `true` with an empty args object while preserving the raw (unparseable) string as `tool_call.arguments`. Because `parse_tool_calls` returns that call, `tool_calls_` is non-empty in `emit_finish`, so the new "parse failed; suppressing buffered tool text" logging never fires for these buffers, and a call whose arguments are not valid JSON is emitted to clients as a valid tool call. Confirm this is the intended Stage-3 behavior; if the goal is only better diagnostics, consider keeping the suppression for unparseable argument strings.</comment>

<file context>
@@ -569,82 +569,59 @@ static bool parse_complete_parameter_body(const std::string & body,
+        if (!parsed.is_discarded() && parsed.is_object()) {
+            out_args = std::move(parsed);
+        } else {
+            out_args = json::object();
+        }
+        return true;
</file context>

[dpavlin]

@cubic-dev-ai review

[cubic-dev-ai]

@cubic-dev-ai review

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[cubic-dev-ai]

All reported issues were addressed across 6 files

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>