Gap A PR1: diagnostic-emission intent + Bash realization (emit(EmitDirective, Bash) → echo >&2); delete dead render_log_annotation

[briansrls]

What

Gap A (emission = ingestion⁻¹ past syntax, docs/plans/emission-ingestion-inverse.md §4(A)) — PR1: the Bash-medium foundation. Introduces the medium-agnostic diagnostic-emission intent and its first row-driven realization, and deletes the dead hand-rolled forward emitter it replaces.

• Intent (src/v2/std/diagnostic.dag): DiagnosticSeverity = SeverityError | SeverityWarning + a thin EmitDirective { severity, message: String } + eq fns. Medium-agnostic, dispatch-free (DESIGN §3). This is the "emit a diagnostic" intent, distinct from the rich compiler Diagnostic.
• Bash realization (src/v2/extdeps/languages/bash.dag): emit(EmitDirective, Bash) → 'echo' '<message>' >&2, row-driven through the shared grammar machinery (emit = serialize_target ∘ translate, DESIGN §4) — not a hand-rolled emitter. Adds the >&2 (StdoutToStderr) fixed redirect token (bash-arc is parked, so absorbed here).
• Witness (src/v2/compiler/manual/emit_directive_bash_test.dag): the live by-execution consumer grounding the intent.
• Deletes the dead render_log_annotation forward emitter (dsl/extdeps/github/log_annotations.dag) + its actions.dag re-export. It was dead (only re-exported, never called); per DESIGN §5 dissolving dead code is spec-without-execution, so it is removed as a dead scaffold, not migrated. The LogAnnotation model + prefix data are kept for the GHA-as-Node arc.

Why

render_log_annotation was a match→concat("::error::", …) forward emitter — the exact thing the language layer abolished (one grammar read backward, N+M not N×M). This lands the agnostic intent + Bash realization so future consumers author intent and emit renders the medium, under bright-gull's MediumStructureLeak lens (#5500).

Honest scope (deferred payoff is markered, not silent)

The Bash transport is severity-invariant (POSIX sh has no severity concept; the stream is the only axis). So in PR1 severity is carried by the intent but realized only by a later medium layer. Phase 2 (witty-wolf GHA-as-Node-gated), markered in diagnostic.dag:

• severity realization (::error/::warning GitHub-Actions annotation over the Bash transport),
• source locus (Optional<Locus>, added with the GHA realizer that reads it),
• migrating the live consumers (tools.build_step ::error, gunbc.ci_spec ::warning) onto emit(EmitDirective, GHA-over-Bash), which shrinks the §0 realization-vocab containment roster (the bright-gull dissolve-on).

Notice is intentionally absent — zero live consumers (only the dead AnnotationNotice), so adding it now would be §5 spec-without-execution.

Test plan (green by execution — gunbc run --claim-run, both source roots)

• emit_directive_bash_error_emits_echo_stderr_holds → true (keystone: exact bytes 'echo' 'build verification failed' >&2)
• emit_directive_bash_severity_invariant_holds → true (Error/Warning render identically; severity is GHA-layer)
• emit_directive_bash_message_flows_holds → true (distinct message → distinct correct bytes; word not fabricated)
• emit_directive_bash_to_stdout_wrong_ne_correct_holds → true (discriminating RED: stdout/no->&2 model emits different bytes; >&2 is load-bearing)
• Regression: existing bash_emit_command_accepts_holds → true; ci_runner_seam_holds (imports actions.dag) → true after the deletion.

Built gunbc release; no .rs changes (fmt/clippy unaffected).

Note: the MODELING-COHERENCE per-head check is failing on a pre-existing ctrl plan-lib circular dependency (plans.coherence → plans.reducible, missing std.reducible) — cites only /home/briansrls/ctrl/plans/ files, identical across commits before/after this PR's edits, unrelated to these gunbc changes.

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