Emit-determinism floor gate: raw 'gunbc compile dsl --target rust' corpus x2 diff=0 — the durable wall regen --verify structurally CANNOT be (rustfmt-masks it + both .rs/.dag are no-sort). Host-side effectful batch-2 gate (spawn compiler twice + diff trees, NOT a pure test fn; structure it like the

[briansrls]

Summary

Adds EmitDeterminismGate as a batch-2 CI floor gate: runs gunbc compile --source-root dsl --dependency-pool-index primary-precedence --target rust twice on the dsl corpus, writes each output to a mktemp -d tree, and asserts diff -r exits 0. Any nondeterminism in the emitter — variant-owner disambiguation order, map-key sort order, import-set ordering — makes the two trees diverge and the gate exits 1.

Corpus scope: dsl only. witness_layer_roots ([dsl, src/v2]) is the witness-discovery roster, not a whole-tree emit target. src/v2 contains intentionally-invalid negative-test fixtures (e.g. bogus_scheme/plant.dag) that fail compilation by design; including them would make the gate permanently RED. The dsl corpus is the correct emit-determinism target: it is not rustfmt-normalized, so raw ordering churn is visible, and src/v2's emit determinism is already covered by the regen_stage0 --verify seed path.

This is the durable wall that regen --verify structurally cannot be: regen_stage0 --verify byte-compares the committed seed against a single-pass regen, but rustfmt normalises whitespace/order in the committed .rs files, and both .rs and .dag outputs are produced by map-iteration that is not guaranteed sorted. Comparing two fresh runs from the same binary eliminates those masking effects and catches true non-determinism by construction.

The gate is wired identically to RegenVerifyGate: gate_runnable_profile classifies it heavy_whole_tree_resolve=true, spawns_host_compiler=true, memory=per_shard+host_compiler. The shell transport is modelled through the extdeps.languages.bash.program bash AST and rendered via serialize_bash — not a hand-written string. Carries Scaffold { dissolves_to: RealizationDispatch, bind: serialize_bash } disposition per §6.

Test plan

A — GREEN: current main, dsl corpus × 2, diff = 0

$ ROOT=/home/briansrls/.worktrees/smart-newt-232
$ GUNBC=$ROOT/target/release/gunbc   # built from d60dc964b6 (this branch head)
$ OUT1=$(mktemp -d) && OUT2=$(mktemp -d)
$ $GUNBC compile --source-root dsl \
    --dependency-pool-index primary-precedence --output-dir "$OUT1" --target rust
resolved 624 sources (transitive import closure)
compiled: 631 files emitted, 0 diagnostics
$ $GUNBC compile --source-root dsl \
    --dependency-pool-index primary-precedence --output-dir "$OUT2" --target rust
resolved 624 sources (transitive import closure)
compiled: 631 files emitted, 0 diagnostics
$ diff -r "$OUT1" "$OUT2" && echo "DIFF=0 GREEN"
DIFF=0 GREEN

B — RED: pre-#5913 binary (fierce-badger-409 @ 8e47a4d), dsl corpus × 2, diff ≠ 0

$ GUNBC_PRE=/home/briansrls/.worktrees/fierce-badger-409/target/release/gunbc
$ OUT1=$(mktemp -d) && OUT2=$(mktemp -d)
$ $GUNBC_PRE compile --source-root dsl \
    --dependency-pool-index primary-precedence --output-dir "$OUT1" --target rust
compiled: 631 files emitted, 0 diagnostics
$ $GUNBC_PRE compile --source-root dsl \
    --dependency-pool-index primary-precedence --output-dir "$OUT2" --target rust
compiled: 631 files emitted, 0 diagnostics
$ diff -r "$OUT1" "$OUT2"
diff -r .../src/extdeps_cache_buildbuddy.rs .../src/extdeps_cache_buildbuddy.rs
58c58
<   ) -> Rc<(... AuthScope, ...)> {
---
>   ) -> Rc<(... Rc<AuthScheme>, ...)> {
# ... (exit code 1 → set -e aborts → result.success=false → gate RED)

The gate catches the variant-owner disambiguation nondeterminism that #5913 fixed: AuthScope vs Rc<AuthScheme> flips between runs with the pre-fix binary.

• Tested GREEN direction locally (dsl corpus × 2 diff = 0 on current main)
• Tested RED direction locally (pre-Ground emit-path variant-owner determinism in .dag authority #5913 binary produces nonzero diff → gate exits 1)
• No new Rust changes — purely additive .dag wiring