Fix DagProcessor crash: add missing name_is_otel_safe() guard to gauge() and timer()

[ersalil]

Summary

SafeOtelLogger.gauge() and timer() were missing the name_is_otel_safe() guard that incr(), decr(), and timing() all have. A DAG filename containing a space (e.g. PBI_SKU_Performance copy.py) caused the DagProcessor to crash on every loop iteration when OTel metrics were enabled.

Why

The DagProcessor emits a gauge metric for every known DAG file on every parsing loop:

Stats.gauge(f"dag_processing.last_run.seconds_ago.{file_name}", seconds_ago)

gauge() only validated against the allow/block list (metrics_validator.test()), which does not check OTel naming rules. A filename with a space passed that check and reached meter.create_gauge() inside the OTel SDK, which raised a plain Exception that propagated uncaught and crashed the process:

Exception: Expected ASCII string of maximum length 63 characters but got airflow.dag_processing.last_run.seconds_ago.PBI_SKU_Performance copy

Note: the OTel SDK error message says "63 characters" but this is a stale message — the actual SDK validation regex allows up to 255 characters (matching OTEL_NAME_MAX_LENGTH). The real rejection reason is the space character, which is not a valid OTel instrument name character. See open-telemetry/opentelemetry-python#3442.

The same gap existed in timer(): it had no validation at all before being passed to _OtelTimer, which would then call record_histogram_value() with the invalid name at .stop() time.

Fix

Added metrics_validator.test(stat) and name_is_otel_safe(self.prefix, stat) to gauge() (both the stat and back_compat_name paths) and timer(), making all five recording methods consistent:

Method	Guard before	Guard after
incr()	✅ both checks	✅ unchanged
decr()	✅ both checks	✅ unchanged
timing()	✅ both checks	✅ unchanged
gauge()	❌ validator only	✅ both checks
timer()	❌ none	✅ both checks

Testing

• test_gauge_with_invalid_stat_names_skipped_without_raising — covers the exact reported scenario (space in filename) and non-ASCII, both reproducing the DagProcessor crash path.
• test_timer_with_invalid_stat_name_does_not_record — covers non-ASCII and space for the timer path.

$ pytest shared/observability/tests/observability/metrics/test_otel_logger.py \
    -k "invalid_stat_names or invalid_stat_name" -v

test_gauge_with_invalid_stat_names_skipped_without_raising[...PBI_SKU_Performance copy] PASSED
test_gauge_with_invalid_stat_names_skipped_without_raising[...mein_däg_file]            PASSED
test_timer_with_invalid_stat_name_does_not_record[...preço_task.duration]              PASSED
test_timer_with_invalid_stat_name_does_not_record[...task copy.duration]               PASSED

========================= 4 passed in 0.14s =========================

closes: #68282

Was generative AI tooling used to co-author this PR?

• Yes — Claude Code (Sonnet 4.6)

This PR was prepared with Gen-AI assistance (Claude). I reviewed all generated code.

[kaxil]

Static checks are failing:

    shared/observability/src/airflow_shared/observability/metrics/otel_logger.py:203: error: Argument 1 to "test" of "ListValidator" has incompatible type "str | None"; expected "str"  [arg-type]
                return bool(stat) and self.metrics_validator.test(stat) and name_is_otel_safe(self.prefix, stat)
                                                                  ^~~~
    shared/observability/src/airflow_shared/observability/metrics/otel_logger.py:203: error: Argument 2 to "name_is_otel_safe" has incompatible type "str | None"; expected "str"  [arg-type]
                return bool(stat) and self.metrics_validator.test(stat) and name_is_otel_safe(self.prefix, stat)
                                                                                                           ^~~~
    Found 2 errors in 1 file (checked 20 source files)