docs: add W1 output producer contract blocker

docs/briefs/r3-evaluator-dispatch.md

@@ -172,6 +172,13 @@ records the current post-bundle state: `AlgebraicLaw::Associativity` and
 declared producer identity / observation-channel authority for executable
 runner work.
 
+**W1 blocker/proposal:** [`r3-pr-e8-w1-output-producer-contract-blocker.md`](r3-pr-e8-w1-output-producer-contract-blocker.md)
+records the accepted STOP+PING for
+`DifferentialEquals(rust_emit_output, dag_eval_output, ProgramOutputBind)`:
+`dag_eval_output` is plausible through no-memo eager `evaluate_body`, but
+`rust_emit_output` still needs an explicit producer identity contract and typed
+observation normalization before runner code can land.
+
 **STOP+PING:** no convention-only stdout parsing, no new `TestPredicate`
 variants, and no permanent expansion of `test_runner.rs` authority without a
 dissolution hook.

docs/briefs/r3-pr-e8-runner-extensions-continuation-readiness.md

@@ -59,6 +59,8 @@ authority for W1 without implementing it:
 
 That follow-on can be docs-only now. A runner implementation should wait until
 the producer identity and observation channel contracts are live and cited.
+The W1-specific blocker/proposal is recorded in
+[`r3-pr-e8-w1-output-producer-contract-blocker.md`](r3-pr-e8-w1-output-producer-contract-blocker.md).
 
 ## Workstream Gates
 

docs/briefs/r3-pr-e8-w1-output-producer-contract-blocker.md

@@ -0,0 +1,121 @@
+# PR-E E8 W1 - Output producer contract blocker
+
+**Status:** BLOCKER / PROPOSAL - docs-only. This note converts the W1
+STOP+PING for `DifferentialEquals(rust_emit_output, dag_eval_output,
+ProgramOutputBind)` into a narrow producer-contract proposal. It does not
+change `test_runner.rs`, rewrite fixtures, add substrate shapes, add
+`TestPredicate` variants, or execute the L4 corpus.
+
+**Parent authority:** [`r3-evaluator-dispatch.md`](r3-evaluator-dispatch.md)
+E8 - Runner Extension Follow-Ons and
+[`r3-pr-e8-runner-extensions-continuation-readiness.md`](r3-pr-e8-runner-extensions-continuation-readiness.md).
+
+**Verification signal:** [PR #1482](https://github.com/gunb-ai/gunbc/pull/1482)
+re-audits Lane 1 after PR-E E5 and identifies W1 runner-extension wiring as
+the concrete gate before Lane 1 can consume the authored L4
+`DifferentialEquals` row.
+
+## Current Live State
+
+`dag_eval_output` is plausibly available enough for a first no-memo eager
+slice. The compiler exposes `evaluate_body` / `eval_node` over the PR-E body
+evaluator spine, and the no-memo eager carve-out is an explicit candidate in
+the Lane 1 re-audit. A future implementation can evaluate the bind named by
+`ProgramOutputBind.output_ref` through the existing evaluator entry, with memo
+semantics deferred for slice 1 and named in the runner arm's dissolution target.
+
+`rust_emit_output` remains blocked. It requires emission, Rust compilation,
+target execution, and normalization of the produced output into the same
+typed value domain observed by `dag_eval_output`. Current main has
+`ProgramObservation<Carrier> { observed: Carrier }`, but that envelope is
+producer-neutral. It does not identify the producer, target language,
+observation channel, exit-status policy, or parse / normalization rule.
+
+The existing L4 fixture declarations for `rust_emit_output` and
+`dag_eval_output` are still `miss_int_lookup()` stubs. Replacing those stubs
+inside the runner by matching declaration names would make
+`test_runner.rs` a second producer language unless the identity contract is
+declared up front.
+
+## Minimum Producer Contract
+
+Before runner implementation, W1 needs an explicit answer to how a
+`DeclarationRef` in `DifferentialEquals` becomes a supported producer.
+
+Two acceptable contracts are possible:
+
+1. **Transitional DeclarationRef-name contract.** The runner may recognize the
+   declaration names `rust_emit_output` and `dag_eval_output` as a temporary
+   producer identity contract only if the implementation comment points here,
+   rejects any other declaration name fail-closed, and names the dissolution
+   target. This is the smallest implementation unblock, but it must be
+   explicitly marked as transitional debt rather than treated as substrate
+   authority.
+2. **Substrate producer role / marker contract.** A P1 substrate proposal adds
+   producer roles or markers that declarations inhabit, so the runner selects
+   producers by typed role instead of declaration spelling. This is the durable
+   direction and avoids name-keyed dispatch, but it is not in scope for a
+   docs-only runner-readiness PR.
+
+Either path must keep the existing `DifferentialEquals` and
+`ProgramOutputBind` surfaces. W1 does not require a new predicate variant,
+new `ProgramInputRole`, fixture-local producer enum, or broad target
+enumeration.
+
+## Typed Observation Normalization Options
+
+W1 also needs an explicit observation-channel rule for Rust output into
+`ProgramObservation<Value>`.
+
+Acceptable options:
+
+1. **P1 typed observation-channel carrier.** A substrate proposal introduces
+   the observation channel and expected value kind, for example stdout vs a
+   declared file plus `ValueKind::Int` / `Bool` / record. The runner then reads
+   the declared channel and normalizes into `ProgramObservation<Value>`.
+2. **Transitional Int-only stdout parse carve-out.** The runner may capture
+   emitted Rust stdout, require a single trimmed integer token, convert it to
+   `Value::LiteralValue(LiteralBits::Int)`, and reject everything else
+   fail-closed. This carve-out is acceptable only if it is explicitly
+   authorized as W1 slice-1 debt, restricted to the L4 Int output fixture, and
+   marked with its dissolution target.
+
+The dissolution target for any Int-only stdout carve-out is the same one named
+by the E8 bundle: PB-Runtime-generated target-language tests and a substrate
+owned observation-channel/value-kind surface replace runner-local stdout
+parsing. Once that surface lands, the runner must stop treating stdout parsing
+as producer authority and read the typed observation fact instead.
+
+## Implementation Fire Criteria
+
+A W1 runner implementation may proceed only when all of these are true:
+
+1. Producer identity is declared by either the explicit transitional
+   DeclarationRef-name contract or a substrate role / marker surface.
+2. Rust output observation is declared by either a typed observation-channel
+   carrier or the explicitly scoped Int-only stdout parse carve-out.
+3. `dag_eval_output` uses the real body evaluator entry with no-memo eager
+   semantics stated at the call site; it does not call fixture
+   `miss_int_lookup()` behavior.
+4. Every new runner arm names its dissolution target:
+   `rust_emit_output` dissolves into PB-Runtime generated target-language
+   tests; `dag_eval_output` dissolves into PR-B eager evaluation plus witness
+   construction.
+5. Unknown producer pairs, unsupported value shapes, failed Rust execution,
+   parse failures, and evaluator errors all remain fail-closed typed runner
+   errors.
+
+Until those criteria are met, `eval_differential_equals` should continue to
+return `NotYetImplemented` for `(rust_emit_output, dag_eval_output)` rather
+than inventing local name dispatch or stdout conventions.
+
+## Explicit Non-Goals
+
+- No `test_runner.rs` changes in this blocker PR.
+- No fixture rewrites and no replacement of `miss_int_lookup()` stubs.
+- No new `TestPredicate`, `Value`, observation carrier, or substrate role in
+  this slice.
+- No L5 corpus execution, broad target enumeration, E6/E7 witness work, or
+  cross-target byte / string comparison.
+- No permanent runner authority. W1 remains transitional runner debt with a
+  named dissolution path.