[chagui]

On bazel run invocations Bazel emits ExecRequestConstructed carrying the final argv, working directory, environment, env-vars-to-unset, and whether the process will actually exec. The PR exposes those on five always-on counts/booleans plus four PII-gated detail attributes so bazel run traces are self-describing without operators having to correlate by command name. bazel build / bazel test invocations emit nothing here.

Review-driven design choices

• Late post-flush path is the production path, not defense-in-depth. Bazel's BEP proto explicitly places ExecRequestConstructed "after a successful build and before trying to execute" — i.e. it can arrive after BuildFinished on the wire. The receiver handles both orderings: pre-flush, attrs land on the root bazel.build span (current design); post-flush, the receiver emits a standalone bazel.run child span (parented to the root via traceID/spanID) carrying the same attrs through a new lateRunSpan helper. Without this, every bazel run invocation would silently emit empty bazel.run.* attrs.
• Split IncludeRunEnvironment from IncludeCommandArgs. Run environments routinely carry credentials, tokens, and host-derived secrets that command-line arguments do not. The original PR re-used IncludeCommandArgs for both axes; the gates are now independent so operators can show argv without exposing env, and vice versa. Docstrings and docs/attributes.md are updated accordingly.
• environment_variable_to_clear (proto field 4) emitted. Previously dropped silently — operators saw the env-set list, ran a repro with those vars, and got different behavior because exec also unset others. Now exposed as both a slice and an always-on count.
• UTF-8 validated on every bytes→string cast. pdata accepts arbitrary strings but OTLP/JSON exporters reject invalid UTF-8 and that failure cascades the entire span batch, not just one attribute. Non-UTF-8 entries are silently skipped (one utf8.ValidString guard per cast site).
• Bounded argv/env. argv capped at 200 entries, env at 50, env-to-clear at 50; each value clipped at 256 bytes via the existing truncateAttrValue helper. The always-on count attributes report the full payload size, not the capped slice, so operators see the truth even when emission is clipped.
• Server-side env sort. Bazel emits env in process-environ iteration order, which is not stable across OSes or runs. Sorting by name in the receiver makes downstream queries and diffs deterministic. Also fixed: the test helper no longer sorts on the input side, so any future receiver-side regression surfaces.

Deferred to follow-up

• OTel semconv alignment for argv/env (process.command_args / process.runtime.environment) — separate task, requires schema discussion.
• nolint:gocyclo replacement on eventTypeName with a map[reflect.Type]string — applies project-wide to every dispatch site, scoped out of this PR.

Closes #63.