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Malte UblandClaude Opus 5.5
12a3f8a225
`{ ...u, k: v }` where `u` is a union of records (`{ ...msg, content }` in
a message-mapping switch, `{ ...command, id } as Cmd`, `{ ...base, entries }
as A | B`) is typed by TypeScript as one spread per arm of `u`, but the
frontend mapped the literal to the union and refused with SC2003 ("a spread
merge over union-typed sources"). The only union-source spreads that lowered
were shared-field overrides and the single-record-arm present test.
lowerDistributedUnionSpread builds the literal the way the checker types it.
The source evaluates once into a hidden local; a tag dispatch builds the
running arm's literal with that arm as the spread source, at the destination
arm the discriminant's last writer picks, else the source arm itself, else
the one arm whose keys are exactly the keys the literal writes. Every key a
contributor may write must be a field of the destination, so a genuine merge
(`{ ...http, ...patch }` where the patch can carry a stdio-only key) keeps
the refusal instead of silently dropping keys. A stored source the checker
narrowed converts through the checked re-tag first, so an excluded arm throws
the catchable TypeError.
Cost: the function runs only where lowerObjectLiteral would have refused;
the new `exact` parameter defaults to false and the new
`spreadArmOverrides` map is empty outside the dispatch, so every existing
literal lowers to the same IR.
`fix/records-literals` changes the same field-desugar capture (it adds a
`checkedSpreadSource` block around it). This commit deliberately keeps the
per-arm source as the expression `(lowerer.spreadArmOverrides.get(srcNode)
?? lowerer.lowerExpr(srcNode))` inside that capture, so the merge keeps
records-literals' `let srcLowered` plus its checkedSource block and applies
the override inside the same expression, as the design specifies.
Pi sites: execution.ts:431, agent-session.ts:3795, runner.ts:1048,
model-resolver.ts:216, sdk.ts:324, session-manager.ts:538, rpc-client.ts:577.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>