Pure-function summaries trusted resolved read and write references, but redeclarations, direct `eval`, and classic Script globals can replace a binding without producing such a reference. A later call could therefore be folded according to an earlier empty declaration and lose runtime side effects.

## Example

```js
function foo() {}
eval("foo = () => side_effect()")
foo()
```

Bindings with redeclarations, bindings visible to direct eval, and classic Script-root bindings do not receive a reusable summary; the eval restriction is intentionally non-sticky so removing the final eval can enable the optimization in a later pass. Module and CommonJS bindings retain the existing fold.

The PR tip passed the full `oxc_minifier` suite independently. The completed stack also passed clippy with warnings denied, formatting, minsize and allocation regeneration, and `just ready`.

## Stack

1. **#24636 — function-summary correctness**
2. #24637 — explicit symbol effect types
3. #24638 — grouped reference counts
4. #24639 — merged persistent metadata
5. #24640 — SymbolState facade

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

Pure-call summaries and member-write hazards encoded semantic states through nested `Option` values and independent bitflags. Reviewers had to reconstruct which combinations were valid and which implications producers must maintain.

This introduces `FunctionSummary` for reusable call proofs and an ordered `MemberWriteEffect` for `None < Hazard < MayMutatePrototype`. Prototype mutation is therefore hazardous by construction, the removed bitflag dependency is no longer needed, and producers and consumers share named contracts. Behavior is unchanged relative to #24636.

The PR tip passed the full `oxc_minifier` suite independently. The completed stack also passed clippy with warnings denied, formatting, minsize and allocation regeneration, and `just ready`.

## Stack

1. #24636 — function-summary correctness
2. **#24637 — explicit symbol effect types**
3. #24638 — grouped reference counts
4. #24639 — merged persistent metadata
5. #24640 — SymbolState facade

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

`SymbolValue` exposed three related counters directly, so every consumer had to coordinate read, write, and member-write-target invariants itself.

This groups them in `ReferenceCounts` and exposes factual queries such as `has_single_read` and `has_only_member_write_target_reads`. The existing 48-byte `SymbolValue` layout is preserved, and the refactor does not change minified output.

The PR tip passed the full `oxc_minifier` suite independently. The completed stack also passed clippy with warnings denied, formatting, minsize and allocation regeneration, and `just ready`.

## Stack

1. #24636 — function-summary correctness
2. #24637 — explicit symbol effect types
3. **#24638 — grouped reference counts**
4. #24639 — merged persistent metadata
5. #24640 — SymbolState facade

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

`MinifierState` separately exposed dense per-pass values, sparse persistent metadata, and optional reachability state even though all three are indexed by semantic symbols. Its private-member stack also used symbol terminology despite storing names rather than `SymbolId`s.

This introduces a `SymbolState` facade that documents the three storage lifecycles and forwards their operations while leaving the reachability algorithm in its dedicated module. The class-local tracker is renamed around private-member usage so it cannot be confused with semantic symbol state.

The PR tip passed the full `oxc_minifier` suite independently. The completed stack also passed clippy with warnings denied, formatting, minsize and allocation regeneration, and `just ready`.

## Stack

1. #24636 — function-summary correctness
2. #24637 — explicit symbol effect types
3. #24638 — grouped reference counts
4. #24639 — merged persistent metadata
5. **#24640 — SymbolState facade**

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