[colbymchenry]

stream: ReadableStream in react's Flow files stopped linking to declare class ReadableStream in flow-typed/environments/streams.js. PR #2736 keeps a
type a module doesn't import to its own file, a declaration file or a declare global block, and a Flow library is none of them: a .js script of declare
statements. The types a Flow library declares were lost on every file. PR #2736
never shipped.

Fix: a .js script with a top-level declare statement is a Flow library, its
declare module.exports no CommonJS export, and its top level global to the
JavaScript files Flow reads, which see it as they see a .d.ts. A TypeScript
file doesn't: its ReadableStream is TypeScript's own. A library's own bare
type names are held to the same rule, and a top-level call declare(...) is no
statement.

Validation

• Tests: fail on main, pass here, on this head.
• No extraction change, so nothing to compare between engines.
• A/B against 4499d007:

Repo	Added	Removed	Moved
react, where it was found	207	3	0
metro	174	5	0
excalidraw, vscode-be, express, taxonomy	0	0	0
Controls: flask, gin	0	0	0

All grouped by name and read. react: ReadableStream 82, ConsoleTask 54, AsyncLocalStorage 36, WritableStream 20, ExtensionRuntimePort 13. metro: Buffer 125, Jest's types, http$IncomingMessage, ws$WebSocket. Removed, all false: a Flow library's Function linked to an enum member and to a declare module block's alias, and HTMLElement to a property.

• Index CPU: the six together, median of 3 interleaved: react 131.0 to 132.4 s (+1.1%, rounds spread 112 to 145 s; wall -6.4%), vscode-be 43.8 to 44.0 s (+0.6%), django 68.0 to 66.4 s (-2.3%). Level within noise.
• Suite: the six PRs of this set ran as one stack, 97cd3800, all six on 4499d007: 853 files passed, 6 skipped; 10,610 tests passed, 2 expected fail, 87 skipped, 0 failed; 4 workers, Vitest 4.1.11, CODEGRAPH_KERNEL_EXPECT=1. This PR's own test files pass on this head.

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