Design: emitted crate partition (Rust realization of agnostic compilation-unit shape)

[gunbai-bot]

Design artifact (docs-only) — the Rust workflow-layer half of a shared, target-agnostic compilation-unit contract, interface-locked 2026-07-16 with the language-consolidation lane (eager-ferret-110, who authors the shared home + staffs C as the 2nd realization).

What this is

• Derives the emitted crate partition (which module lands in which crate) — closing stage0_crate_plan()'s hand membership ledger, the last fork #6677 (derived registration) did not cover.
• Policy: crates ≈ cores, even, flat, acyclic; objective = minimize the parallel critical path (the CI-wall "one giant serial crate" symptom).

Layer split (locked)

• Shared home (language lane owns): CompilationUnit + partition_fold(module_dag, Map) -> List<CompilationUnit> + per-target R4 validity interface + agnostic Provenance tag. interface/deps are derived-only (fold is sole producer). C realizes the same home (link-cyclic, include-closure, .h/.c).
• This doc (Rust workflow layer): PartitionParameter/PartitionPolicy/resolve_partition -> Map + Rust R3 linkage + Rust R4 (SCC-atoms/acyclic). Only the resolved Map crosses into the shared fold, so the shared shape never imports the workflow policy (no §3 import-arrow inversion — the F7 class).

Acceptance

Re-anchored on v2.std.determinism/std.perturbation: the partition is a non-semantic perturbation axis; a behavior that depends on it is a determinism leak. Discriminating: a fixed module DAG under ≥2 partitions all build + are behaviorally equivalent; an invalid partition refuses (§5).

Staging

• Phase 0 (unblocks v2 multi-crate self-host): ExplicitPartition interim grouping as a declared scaffold (HandExplicit provenance + dissolution trigger).
• Phase 1: derived balanced PolicyPartition replaces the explicit value (same parameter).

Not blocking / gated on

Implementation is gated on main-green (current compile-clean algebra break; fixes #6705/#6701/#6696 in flight) and operator sign-off on the load-bearing src/v1/stage0_crates.dag touch. Orthogonal to the Wave-2 self-emit fan-out (Band A robust to membership churn). Draft until placement is decided.

🤖 Generated with Claude Code

[gunbai-bot]

Marking ready — the design content is complete and interface-locked with the language-consolidation lane (eager-ferret-110). Note for reviewers: this is a docs-only design artifact; its CI will show red on the inherited main baseline (the compile-clean algebra field-authority break — src/v2/std/{diagnostic,logic,integer}.dag, trigger #6686, fixes #6705/#6701/#6696 in flight), which a docs-only diff can neither cause nor fix. Review the content (esp. §2 layer split and §13 interface summary); the check will green once main greens. Implementation placement (me-dispatched vs. elsewhere) is a pending operator call and does not affect the locked design.