Four-compile redundancy collapse (#4091 §1.2): collapse ci_v4 four 332-source closure compiles to one path (~14m savings)

[briansrls]

Four-compile redundancy collapse (#4091 §1.2) — model-only slice

Sequenced behind #4171 (primary carrier). Intentionally DRAFT per parent's dedup ruling — do not flip ready / merge before #4171 lands. This PR is the complementary modeling-hygiene slice (collapse of the modeled ci_pipeline shadow jobs in src/v4/workflow/ci.dag); #4171 carries the real required-path multi-target-emit win.

What this changes

Three modeled jobs in ci_pipeline each independently re-ran a full src/v4 332-source closure compile while only declaring a bare needs: [v2_compile_src_v4] ordering dep. This turns those into real artifact-consumption edges by adding ci_upsert_upstream_job_input(job: v2_compile_src_v4) to each job's CiUpsertStep inputs — mirroring the established v4_t15 / testclaim_corpus_eval pattern (ci.dag:807, "M1 rust emit is upstream compile authority"):

• m1_rust_emit_probe_execution
• lens_ci_registry_execution
• phase1_nat_semiring_rung_gate_execution

Each consumes v2_compile_src_v4's target-independent resolved closure (front-end shared once) and re-emits its own target from it.

Correctness (manager-requested confirmations)

1. Front-end-only collapse — emit + strictness unchanged. Only the redundant front-end recompile (parse/lower/infer over the 332-source closure) is deduplicated. Each job still re-emits its own target (M1 still --target rust at full V4_M1_RUST_EMIT_PROBE_STRICT=1); no emit target is collapsed into another. Coverage is identical, just deduplicated.
2. Affected-set invalidation unchanged per job. Each job keeps its existing src/v4/** file-set input (and m1 its scripts/v4-m1* / Cargo.{toml,lock}); the upstream edge is added, not substituted. What triggers a rerun is neither widened nor narrowed.

Discipline

• No new ci.dag carrier (existing ci_upsert_upstream_job_input only) — no DFS-arbiter sign-off needed.
• No substrate / generated-CLI / emit-pipeline touch (that is shape B = Four-compile redundancy collapse (#4091 §1.2): single 332-source closure path (~14m) #4171's lane).
• bootstrap-dag split out: v2_bootstrap_smoke_execution's collapse is not a clean modeled edge — the workflow_local_bootstrap_dag_upstream carveout (ci.dag:336) has dissolution_target: ModelMissingSubstrate { what: v4_bootstrap_dag_emit_ci_job } (= substrate). Deliberately untouched; tracked as a follow-up.

Receipt

New integration test v4_workflow_ci_four_compile_collapse_jobs_consume_v2_compile_src_v4_closure block-scopes the assertion that each of the three jobs carries the upstream edge.

Post-#4171 rebase note

After #4171 lands, rebase onto main and drop any model/test edits #4171 already covers; keep only the residue (the shadow-pipeline upstream edges #4171 doesn't touch).

[briansrls]

Closing per CI Manager + smart-newt-797 agreement: model-only slice sequenced behind #4171 (held on #4179/M1-main). Substantial rework expected at rebase — will open a fresh post-#4171 PR from node adhoc-11b7a2da-46a / cool-fox for ci_pipeline residue only.

Tracking node and plan preserved; not abandoned.