What's Changed

filters: tighten maybe_inject_no_stat word-boundary check (#1178, closes #1171): Two confirmed false positives in maybe_inject_no_stat. "gitpull some-arg" matched starts_with("git"), causing --no-stat to be appended to an unrelated binary. "git log upstream/pull/123" matched contains("pull") via the path component, silently suppressing the diffstat. Fixed with a trailing-space word boundary (starts_with("git ")) and a token-level check (command.split_whitespace().nth(1) == Some("pull")).

metrics: add received event at top of each tool handler, guard OTEL histogram (#1181, closes #1177): Emits a result="received" MetricEvent at the very top of each of the seven tool handlers, before any validation or execution. A single metrics lookup can now definitively distinguish failures in the rmcp dispatch layer (no received entry) from handler-level failures (received present, no ok/error). An early-return guard in record_otel_metrics prevents duration_ms=0 events from polluting the latency histogram.

exec: remove redundant child.wait() in no-timeout branch, add exit_code test (#1180, closes #1173): The no-timeout branch called child.wait() twice: once to extract the exit status and again implicitly. The second call was redundant and misleading. Captured exit_status from the first await and reused it throughout. Removed the now-redundant test test_exec_exit_1_no_timeout whose coverage was already provided by existing tests in exec_command.rs.
exec: fix SIZE_LIMIT comment, add heredoc metrics, record injected command on span; add MetricEventBuilder (#1179, closes #1172): Three surgical fixes: the SIZE_LIMIT comment said "50k chars" but the constant is 5_000 bytes; corrected. The validate_heredocs early-return path emitted no metric, making validation failures invisible in JSONL; now emits result="error", error_type="invalid_params". The post-injection command is now recorded on the span before span.record("command", ...). Also adds a fluent MetricEventBuilder to metrics.rs that reduces MetricEvent construction boilerplate across all seven handlers (net -227 lines in lib.rs); no behaviour or schema change.

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