Multiple runtime declarations can share one semantic `SymbolId`, while source-order traversal stores each declaration's constant, boolean-falsy, and fresh-value facts in the same slot. A nested function can consume the first declaration's facts before traversal reaches a later declaration, so invalidating only on the later visit cannot repair an already-applied fold.

This PR checks semantic redeclaration metadata at the first producer. When a binding has multiple runtime value declarations, it withholds all declaration-derived value facts from every producer. Type-only merges remain eligible, and per-symbol reference counts are preserved.

## Example

```js
export function f(a) {
  if (a) var x = true;
  else var x = false;
  return x ? "ok" : "fail";
}
```

After this PR, minification preserves the branch-dependent test:

```js
export function f(a){if(a)var x=!0;else var x=!1;return x?`ok`:`fail`}
```

The rule is deliberately conservative. It also protects member writes when one declaration may alias an external object, but it gives up valid source-order folds such as `var x = 1; var x = 2; return () => x`. A regression test pins that behavior. Recovering same-value or otherwise benign redeclarations would require reaching-definition or dominance analysis rather than this source-ordered fact cache.

The check only covers declarations sharing one `SymbolId`. Sloppy Annex B block functions can update an existing `var` through a separate semantic symbol; current `main` and this stack still mishandle that pre-existing case, tracked in #24659.

Together with required lower PR #24650, this makes cached declaration facts conservative for conditional positions and same-symbol redeclarations.

The full `oxc_minifier` suite passes with 621 tests and 42 ignored; clippy, formatting, the #24603 runtime and repeat-compression repros pass, and regenerated minsize and allocation snapshots are byte-identical.

Fixes #24603.

## Stack

1. #24650 — conditional `var` initializer facts
2. **#24658 — redeclared binding facts**

Implemented with AI assistance (Claude Code and OpenAI Codex). The contributor remains responsible for reviewing, understanding, and submitting the changes under the repository AI usage policy.

### 💥 BREAKING CHANGES

- 54cc121 ast: [**BREAKING**] Split `MetaProperty` into `ImportMeta` and
`NewTarget` (#24557) (camc314)

### 🚀 Features

- 4c71560 parser: More friendly error for spread element in dynamic
imports (#24705) (sapphi-red)
- 7b045cd minfier: Drop last break from last switch case (#24673)
(Armano)
- 7d3c178 minifier: Remove unreachable recursive functions (#24125)
(Dunqing)
- 94f99b3 ast: Allow `NONE` to be passed to AST builder methods where
`Option<ArenaVec>` is expected (#24629) (overlookmotel)
- 77230c5 ast: Accept arrays for `ArenaVec` params of AST builder
methods (#24621) (overlookmotel)
- f08b152 allocator: Implement `FromIn` for array to `Vec` conversion
(#24620) (overlookmotel)
- 2338c13 track-memory-allocations: Track heap deallocs, alloc bytes,
and peak growth (#24619) (Boshen)
- 7aa4739 syntax,transformer: Move JSX entity decoder to `oxc_syntax`
(#24617) (camc314)
- 2b097c4 str: Export `Str` as `ArenaStr` (#24604) (overlookmotel)
- 3acf4c1 minifier: Expand switch optimiation to remove empty cases
(#24520) (Armano)
- 129b759 parser: Improve diagnostics for unparenthesized LHS on
exponential expr (#24569) (camc314)
- 4d0c601 minifier: Fold arithmetic over undefined and null operands
(#24485) (Dunqing)
- 91541dd minifier: Drop empty switch statements  (#24527) (Armano)
- d05224d ast_visit: Generate VisitJs visitor that skips TypeScript
type-space (#24499) (Boshen)
- 3d22307 parser: Add `ParseOptions::enable_ident_hashes` (#24491)
(Boshen)

### 🐛 Bug Fixes

- 64c2241 minifier: Align class heritage removal with assumptions
(#24533) (Dunqing)
- 48b59f4 parser: Span ambient generator diagnostics (#24711) (camc314)
- e750a82 ecmascript: Fix false negative for may_have_side_effects on
dynamic property access (#24709) (sapphi-red)
- f145d73 minifier: Guard reordered identifier reads (#24698) (Dunqing)
- a2ef382 isolated-declarations: Reject `window.Symbol` as global symbol
reference (#24689) (camc314)
- b1bcf72 minifier: Invalidate facts for redeclared bindings (#24658)
(Dunqing)
- 921b834 minifier: Don't treat a conditionally-assigned var as
write-once (#24650) (Dunqing)
- 061af1f minifier: Avoid stale pure function summaries (#24636)
(Dunqing)
- 40c2f43 allocator: `Vec::from_array_in` do not allocate zero-length
array (#24628) (overlookmotel)
- 70994ae codegen: Preserve comments before expression operands (#24510)
(Dunqing)
- 7b4baff parser: Reject new import member access (#23459) (camc314)
- 128b385 minifier: Clippy warning with no-debug-assertions (#24547)
(camc314)
- 8421feb parser: Use first `as` span for imported name (#24537)
(leaysgur)
- c517aa0 parser: Reject invalid accessor assertions (#24504) (camc314)

### ⚡ Performance

- 884d9eb parser: Pre-size cover-grammar assignment target buffers
(#24683) (Boshen)
- d3f07a0 diagnostics: Box OxcDiagnosticInner to reduce binary size
(#24665) (Boshen)
- bcc9de0 parser: Defer diagnostic creation until parse exit (#24663)
(Boshen)
- c35d8ab allocator: Mark `ReplaceWith` panic path cold (#24515)
(camc314)
- ba65790 semantic, allocator: Branchless `clone_in` for semantic IDs
(#24564) (overlookmotel)
- 747feec parser: Build AST nodes with the AST builder instead of
cloning (#24540) (Boshen)
- ba35a0d react_compiler: Use IndexVec for dense id-keyed maps (#24549)
(Boshen)
- b685062 react_compiler: Keep small hot-path collections inline
(#24514) (Marius Schulz)
- a149e95 transformer: Outline rare expression exits (#24512) (camc314)
- 7808a6e react_compiler: Make aliasing effects cheap to intern and
clone (#24506) (Marius Schulz)
- 3a36f2a react_compiler: Store AbstractValue reasons as a u16 bitmask
(#24480) (Boshen)
- 1c96753 react_compiler: Use FxHashMap for the lookup-only aliasing
node map (#24490) (Boshen)

Co-authored-by: Cameron <[email protected]>