# S0.2 — E6b disposition, the two-corpus partition, and the E6BR-5 re-file

Authority: `runs/stdlib/design/fork-c-plan/planspec-r3.json` (S0.2) +
`runs/stdlib/design/fork-c-deepdive/reconciled.md` (§3 one-resolver-two-timings, §6
roadmap, §8 fold-in). Base: `wt-stdlib-base @ 1f75528` (A–E6a merged). E6b:
`flow/stdlib/E6b @ af737b0` (PAUSED, unmerged). This is documentation only — no
production code change.

## 1. E6b transitional src is NOT merged

The transitional E6b source on `flow/stdlib/E6b @ af737b0` is **not** brought onto the
Fork C baseline. All of it is destined for **S3/S6 deletion** under Fork C:

- the **route-all engine** + the type-reference **choke-point**
  (`resolveRegistrationSigTypeInSource` / `sig_registration_mode`) — `lower.zig`,
  `protocols.zig`;
- the executable **grep gate** `src/ir/e6br_gate.test.zig` (+ its `ir.zig` import);
- the supporting `calls` / `lower` / `protocols` / `type_bridge` / `type_resolver` /
  `types` changes.

Grounded reasons it is transitional, not load-bearing: the whole-AST resolver walks
**every** reference position, so it closes the protocol/param-impl signature surface
the choke-point policed (reconciled §3/§4 T4); and the grep gate is unnecessary once
the leaf it polices no longer exists (reconciled §5). A–E6a stays merged purely as
**proof-of-semantics + per-decl nominal infra** (`internNominal` / `nominal_id==0`
byte-identity rule / `RawDeclRef` facts → the `DeclId` seed) — see
`S0.3-reuse-delete-ledger.md`.

**Grep-clean (verified on this branch — `src/` is base-equivalent, zero src changes):**

| check | base / S0 | E6b |
|---|---|---|
| `resolveRegistrationSigTypeInSource` in `src/` | **absent** | present (`lower.zig`) |
| `sig_registration_mode` in `src/` | **absent** | present (`lower.zig`, `protocols.zig`) |
| `src/ir/e6br_gate.test.zig` | **absent** | present |
| `walkConcreteSigArgs` in `src/ir/lower.zig` | **absent** | present (the E6BR-5 site) |

Because S0 introduces **no production code change**, these remain absent on the Fork C
baseline by construction.

## 2. Harvested resolver-acceptance corpus + the two-corpus partition

Harvested by copying the example **trees + their expected goldens ONLY** (never the
transitional src):

- `examples/0811–0829` (19 trees) from `flow/stdlib/E6b @ af737b0` — error-set /
  protocol / param-impl / route-all same-name ambiguity & own-wins surfaces;
- `examples/0795–0798` (already merged on the base) — the enum/union ambiguous/own-wins
  pair.

The corpus is **partitioned by empirically running each harvested case through the
current base compiler and comparing its output to the E6b TARGET golden** (the exact
method: build, then `sx run examples/<name>.sx`, normalize with the
`run_examples.sh` rules, diff against the E6b golden):

### (a) BASELINE-GREEN — the mirror-equivalence corpus

Harvested cases whose **old selector is already CORRECT on `wt-stdlib-base` today**
(actual == E6b target, byte-for-byte). They get standard
`examples/expected/<name>.{exit,stdout,stderr}` markers, are run by
`tests/run_examples.sh`, and are **locked into the S0 baseline**. This set is the S2
assert-only Debug mirror's **ONLY** oracle.

| case | exit | proof it is already-correct on base |
|---|---|---|
| `0795-modules-same-name-enum-ambiguous` | 1 | already merged + green (E6a) |
| `0796-modules-same-name-enum-own-wins` | 0 | already merged + green |
| `0797-modules-same-name-union-ambiguous` | 1 | already merged + green |
| `0798-modules-same-name-union-own-wins` | 0 | already merged + green |
| `0823-route-all-own-wins-subform-wrappers` | 0 | base output == E6b target (`opt=1 arr=2 sl=3 dep=99`) |
| `0828-protocols-param-impl-arg-wrapped-own-wins` | 0 | base output == E6b target (`tag=7 dep=9`) |

### (b) RESOLVER-TARGET — known-wrong old behavior

Harvested cases (and the re-filed E6BR-5) where the **old selector is wrong on the
E6b-unmerged base** (silently resolves last-wins / under-diagnoses / picks the wrong
author / fails own-author resolution). They are held in a **documented, listed,
separate harness** at `tests/resolver-target/` with **NO active `examples/expected/`
marker** (so `run_examples.sh` does not run them), but **WITH** their TARGET output
recorded and an **enumerated manifest** (`tests/resolver-target/manifest.md`, 18
cases). The sibling xfail runner `run_resolver_target.sh` runs each and asserts it
currently FAILS — so the set is **never silently dropped**. It flips to active + green
at **S3.9**.

The 17 harvested `08xx` resolver-target cases: `0811, 0812, 0813, 0814, 0815, 0816,
0817, 0818, 0819, 0820, 0821, 0822, 0824, 0825, 0826, 0827, 0829`. Per-case class,
base-now behavior, and target are in the manifest.

**0811 and 0829 placement (required one-liners):**

- **0811 → resolver-target.** *Old selector is wrong here on the E6b-unmerged base:*
  the five bare error-set forms (`size_of` / annotation / type-as-value / match-arm /
  `!IoErr` channel) each silently resolved one global last-wins `IoErr` via the
  `type_bridge.resolveInlineErrorSet` `findByName` short-circuit and the program exited
  0; the target is five loud "type 'IoErr' is ambiguous" diagnostics + exit 1.
- **0829 → resolver-target.** *Old selector is wrong here on the E6b-unmerged base:*
  the concrete `*Box` prefix of the mixed pack-closure source fell to the no-author
  `type_bridge.resolveTemplateSignatureType` wrapper (global last-wins) and registered
  silently (exit 0); the target is a loud `Box` ambiguity + exit 1.

## 3. E6BR-5 re-filed into resolver-target

**E6BR-5** (the open nested-pattern ambiguity hole that paused E6b) is re-filed into
the resolver-target set as a regression — **explicitly NOT an E6b attempt-6.**

- *What it is:* `walkConcreteSigArgs` (E6b `lower.zig:14686`) **skips** any direct arg
  that has an unbound part instead of **recursing** into it, so a nested concrete leaf
  (`*Box` inside `Closure(Closure(*Box, ..$inner) -> $IR, ..$args) -> $R`) is never
  ambiguity-checked; the impl compiled rc=0. On `wt-stdlib-base` (E6BR-4 unmerged) both
  the direct and nested concrete leaf silently resolve via the pre-E6BR-4 no-author
  wrapper path, so the reproducer exits 0 with no diagnostic.
- *Subsumption (one line):* the whole-AST resolver walks **every** reference position —
  including nested parameterized-pattern leaves — so the nested `Box` is
  ambiguity-checked by construction and the "skip a nested arg" hole cannot exist.
- *Form:* an authored reproducer lives at
  `tests/resolver-target/cases/e6br5-nested-pack-source-ambiguous.sx` (self-contained;
  verified to exit 0 silently on the base — the fail-before). Its target is a **spec**
  (exit 1 + `Box` ambiguous), with exact bytes produced by the resolver at S3.9
  (`expected/e6br5-…target.md`).

## 4. The mirror / flip statement (locked)

- **S2's mirror asserts `resolver == old-selector` over the BASELINE-GREEN corpus
  ONLY.** It never asserts new == old over the resolver-target corpus (the old selector
  is a wrong oracle there), and it never selects for lowering (assert-only, Debug-only,
  deleted in the S3.10 commit that completes the cutover).
- **S3.9 flips the resolver-target corpus to active + green**, validated against each
  case's TARGET output (not against the old selectors). After the flip, the goldens
  move from `tests/resolver-target/expected/` to `examples/expected/`, the harness goes
  empty, and these cases stay green through S6.

## 5. Acceptance (S0.2) — self-check

- ✅ Written disposition: E6b transitional src not merged (§1, grep-clean table).
- ✅ Harvested corpus recorded + partitioned: baseline-green (markers, locked,
  mirror-equivalence) vs resolver-target (enumerated manifest, separate listed harness,
  no active marker, TARGET goldens present, currently xfail, never dropped) — §2.
- ✅ 0811 and 0829 each in resolver-target with the "old selector is wrong on the
  E6b-unmerged base" one-liner — §2.
- ✅ E6BR-5 re-filed into resolver-target with the subsumption one-liner, NOT an E6b
  attempt-6 — §3.
- ✅ Mirror/flip statement recorded — §4.
- ✅ No transitional E6b src on the Fork C baseline (grep-clean) — §1.
