fix(typescript): await getNextPage() in generated pagination snippet

[devin-ai-integration]

Description

Linear ticket: Refs

The manual page-by-page pagination example emitted into generated TypeScript SDK README.md / reference.md / snippet.json did not type-check (reproduced on generator 3.88.3):

let page = await client.item.listActivity();
while (page.hasNextPage()) {
    page = page.getNextPage(); // TS2740: Type 'Promise<Page<...>>' is missing ... from type 'Page<...>'
}

Root cause: the snippet is not a text template — it is built as a TypeScript AST in maybeLeverageInvocation in GeneratedDefaultEndpointImplementation.ts, which created the assignment RHS as a plain createCallExpression for page.getNextPage(). The pagination runtime (Page.getNextPage() and CustomPager.getNextPage()) is async and returns Promise<this>, so assigning its result back into the Page-typed page variable is a type error. The neighbouring for await (const item of pageableResponse) snippet is generated separately and was always correct, which is why only the manual loop was broken. The fix wraps the call in ts.factory.createAwaitExpression, emitting page = await page.getNextPage(); (the enclosing snippet is already an async context, since the initial await client...() call is emitted there too).

Changes Made

• Emit page = await page.getNextPage(); from the pagination leverage-code AST in GeneratedDefaultEndpointImplementation.maybeLeverageInvocation.
• Updated the client-class-generator snapshot for the leverage-code test.
• Regenerated 83 ts-sdk seed outputs (README, reference, snippet.json) across all pagination fixtures.
• Added an unreleased TypeScript SDK changelog entry.
• Updated README.md generator (if applicable)

Audit of sibling snippets / other languages

• Binary-response snippets check out against BinaryResponse: the active stream() assignment is synchronous, and the arrayBuffer() / blob() / bytes() alternatives are shown as awaited comments.
• The async-iterator pagination snippet is correct as-is.
• Other generators do not have the analogous defect: Java's SyncPage.nextPage() returns SyncPage<T> synchronously; Go's example already uses page, err = page.GetNextPage(ctx) with error handling; Python (iter_pages()), PHP (getPages()), C#, Rust and Swift pagination sections don't use this direct-async-assignment shape.

Testing

• Unit tests added/updated — client-class-generator (612 tests) and TS generator (186 tests) suites pass; leverage-code snapshot now asserts the awaited form.
• Manual testing completed — pnpm compile, pnpm seed:build, pnpm lint:biome, pnpm format:fix clean; pnpm seed test --generator ts-sdk --skip-scripts 251/251 passing; no page = page.getNextPage(); remains anywhere under seed/.

Gap: there is no existing test that extracts fenced TypeScript blocks from a generated README.md/reference.md and runs tsc over them. Seed's TS project verification (.fern/verify.sh → pnpm build && pnpm test) compiles the generated SDK and dynamic-snippet tests, but never the documentation snippets, so this class of bug (README-only, non-compiling example code) is currently uncaught by CI. The snapshot test added here pins the exact generated text, but a real README compile check would need new infrastructure.

Link to Devin session: https://app.devin.ai/sessions/79649fbe4aa54feb8b07597bbf1de100
Open in Devin Desktop: https://app.devin.ai/desktop/session/79649fbe4aa54feb8b07597bbf1de100?variant=devin

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[devin-ai-integration]

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[nitpickybot]

Single-line generator fix wrapping page.getNextPage() in an await expression, plus regenerated seed fixtures and a changelog entry. The AST change is correct and the enclosing snippet is already async (it opens with await client...). No issues found.

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

[github-actions]

SDK Generation Benchmark Results

Comparing PR branch against median of 5 nightly run(s) on main (latest: 2026-08-28T06:31:59Z).

Full benchmark table (click to expand)

Generator	Spec	main (generator)	main (E2E)	PR (generator)	Delta
ts-sdk	square	160s (n=5)	165s (n=5)	150s	-10s (-6.2%)

main (generator): generator-only time via --skip-scripts (includes Docker image build, container startup, IR parsing, and code generation — this is the same Docker-based flow customers use via fern generate). main (E2E): full customer-observable time including build/test scripts (nightly baseline, informational). Delta is computed against generator-only baseline.
⚠️ = generation exited with a non-zero exit code (timing may not reflect a successful run).
Baseline from nightly runs on main (latest: 2026-08-28T06:31:59Z). Trigger benchmark-baseline to refresh.
Last updated: 2026-08-28 16:31 UTC

[devin-ai-integration]

Review — no breaking changes found.

• getNextPage() is public async getNextPage(): Promise<this> in both Page.ts and CustomPager.ts, so the previous snippet page = page.getNextPage() assigned a Promise to a Page variable and did not type-check. The emitted snippet is documentation/reference only, so this changes no generated SDK runtime code and no public API.
• The enclosing generated example is already async, so await is valid there.
• Snapshot and the 83 regenerated seed README/reference/snippet.json outputs are consistent, and no page = page.getNextPage(); remains under seed/.
• Changelog present under generators/typescript/sdk/changes/unreleased/, type fix.

Approving.

Written by Devin