[cramforce]

Reverts #1561 (6bb2711) and keeps its one unrelated fix.

Why

scriptc's premise is that types don't lie. #1561 made a checked cast whose value does not fit its type (JSON.parse(text) as T, const x: T = anyValue) continue in a dynamic copy of the code after it, so a program could keep running on data that contradicts its own types. That was a misdirection: a mismatch should stay a TypeError naming the path, and programs and test fixtures should declare types that match their data. This restores the checked-cast behavior and its documentation (the runtime type checks section, the limitations page and --tier) to what they were before #1561.

What stays

a?.b.c on an any value short-circuits only on the guarded step: it is undefined when a is nullish and throws when a is present but a.b is undefined, as in Node (before #1561 it answered undefined). That piece is re-applied as its own commit with a new corpus program, optional-chain-any-tail.ts, identical to Node in both lanes. corpus/1544-dyn-json-reads.ts keeps its #1561 binary.

Nothing merged after #1561 used it: no references to scr_dyn_check_recover, checked-fallback.ts, the checkedCast.* builtins or the fallback JSON helper remain.

Validation

• Lint, format, pnpm test:ts7 --baselines-only, and the self-host IR build (no diagnostics).
• dyncheck, json-callbacks, native-class-array-boundaries, discriminated-json, json-schema-parse-emission, diagnostics, npm-static and ts7 order parity: 479 passed.
• Differential corpus programs touching JSON, dynamic values and optional chains (plain lane), and the affected programs in the sanitized lane, including the casts added after Continue a failed checked cast with its value in a dynamic tail #1561 (6412-any-valued-dictionaries, caught-system-error-fields, json-typed-parse-index-signatures).
• Zero-cost gate against main (3df33dc), bench + self + corpus shard 1/8 plus every program Continue a failed checked cast with its value in a dynamic tail #1561 had changed: the only differences are programs with checked casts that Continue a failed checked cast with its value in a dynamic tail #1561 had made eligible (bench json-records, intern-table and http-api; self; 12 corpus programs), and those return to the throwing cast and shrink back (http-api 700,200 → 605,752 bytes; 1006-json-fs-config back to its pre-Continue a failed checked cast with its value in a dynamic tail #1561 323,984 bytes). Every optional-chain program, 1544-dyn-json-reads included, is identical. Compile time: bench geomean −0.23%, self-hosted compiler +0.97% (within tolerance).

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated
scriptc	Ready	Preview, v0	Oct 21, 2026 12:43am UTC