fix(ts): contextually type values written into annotated Program types

Parent

• #548
• #416
• Follow-up to #751

Evidence

#751 (8c587f6) projects the members an annotated receiver reads. The mirror position — a value written into such an annotation — still leaves nested callback parameters implicitly any. On the #688 module fixtures (util, errors, schemas), with a consumer that only writes:

import type * as schemas from "./schemas.js";

declare function takesSchema(schema: schemas.Schema): void;

const literal: schemas.Schema = {
  _zod: {
    run: (payload) => {                                   // TS7006 in Home
      payload.issues.push({ code: "invalid_type", expected: "string", input: payload.value });
      return payload;
    },
  },
};

takesSchema({
  _zod: {
    run: (payload) => payload,                            // TS7006 in Home
  },
});

Both engines contextually type payload from SchemaInternals.run. Schema is a projection_only Program export, so the annotation's own type stays any in Home and supplies no contextual type to the object literal's nested members. #751 deliberately did not change this: it resolves members that are read, never the annotation's whole type, because publishing the projection as the declared type added 38 Zod identities (recorded in TS_PERFORMANCE.md).

Fair oracle

Reuse the issue_688_* fixtures in packages/ts_program/src/ts_program.zig. Cover an annotated const initializer, a call argument, a nested property, and a returned literal. Each callback body must read a projected member (payload.issues) so silence is not mistaken for any, and each graph needs a deliberate invalid control.

Acceptance

• TypeScript 6.0.3, tsgo 7.0.2, and Home agree by file, line, column, and code.
• Contextual types only: the projection must not become the annotation's type, and writes must not be checked against an approximate whole type (a regression here shows up as new Zod TS2345/TS2322).
• Exact Zod 4.5.2 core diagnostic identity A/B shows zero additions.
• Full Program/checker suites and optimized builds pass, evidence documented and linked from the README.

Fixed in 168bb2a6a.

What was wrong

#751 made members read through a projection-only imported type resolve. Values written into one still did not, so every callback inside the literal fell back to an implicit any:

const literal: schemas.Schema = { _zod: { run: (payload) => payload } };
//                                             ^ TS7006, both engines report nothing

The fix

The literal takes its contextual target from the type that was written, not from its checked type — walking a binding's annotation, the callee's parameter annotation, or the enclosing literal's member until a reference to an imported declaration is reached. An overload set, or a name that walk cannot resolve uniquely, yields nothing rather than a guess.

Only the member the literal actually writes is lowered, and only as context. The literal's own type and every assignability check still see any — the same scope the read side uses. Publishing the whole projection as the annotation's type was measured and rejected under #751 at +38 Zod identities, because the approximation then becomes an assignment target. Context cannot reject a program that plain any accepted; it only replaces an implicit any parameter with the declared one.

Three-engine agreement

Each callback assigns payload to number, so the single TS2322 proves the declared type arrived rather than an implicit any being silenced.

Zod 4.5.2 core

Removed: core/api.ts:1850:56, core/memoizer.ts:97:9, 97:16, 97:25, 107:9, 121:10 — all TS7006. Both are the targeted shape: const memo: $ZodMemoizer = { alloc(_inst, payload, empty) { ... } } and const def: schemas.$ZodCustomStringFormatDef = { fn: (val) => ... }.

Worth stating plainly: both pinned engines report exactly one diagnostic on this graph (the locales module the shard omits) and no TS7006 anywhere. So every diagnostic Home still emits here is a false positive, and the six removals are unambiguous rather than a judgement call.

Scope of the measurement

The Zod figures cover the 21 src/v4/core/**/*.ts files only. The pinned tree's src/v4/locales shard was deleted by the host's periodic /private/tmp cleanup during #751, so that shard's identities are unmeasured. The corpus is now kept outside /tmp.

Program 213/213, checker 4371/4371, ReleaseSafe and ReleaseFast builds, zig fmt --check and git diff --check clean. The added test fails against 8c587f6fb with TS7006 at each of the three positions, so it discriminates. No timing is claimed (#548).

Closing as completed. The implementation and full acceptance evidence landed in 168bb2a and are ancestors of current origin/main: three-engine contextual-typing agreement, permanent positive/negative controls, zero added Zod identities, and passing Program/checker/build gates are recorded above.