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.

Pure-call summaries and member-write effects used separate sparse hash maps even though both are keyed by `SymbolId` and remain valid across peephole iterations.

This stores both values in one `PersistentSymbolMetadata` entry. Summary replacement and monotone member-effect strengthening remain independent, and clearing a dynamic-binding summary updates an existing entry without allocating or discarding its member effect.

The regenerated allocation snapshot records fewer system allocations: checker 155→152, pdf 2469→2467, antd 1044→1038, and kitchen-sink 1872→1867. `minsize.snap` remains byte-identical.

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.