[ochafik]

Motivation

Apps that produce or edit documents (editors, annotators, generators) need a way to hand their current output file back to the model. ui/download-file saves to the user's disk without the model ever seeing the bytes, and waiting for a tool call to finish doesn't fit a long-running editor whose output materializes when the user is done editing.

A simple pattern covers this: the app exposes a "get output file" tool that returns the current document as an embedded resource in the tool result. The model learns of the file through a call it made itself, and gets the bytes in the same result. This PR adds that pattern to the pdf-server example — on both tool surfaces, so it works with hosts that call view-registered tools directly and with hosts that only drive server tools (e.g. Claude Desktop over stdio).

Changes

• get_current_pdf app tool (view-registered via app.registerTool): returns the currently displayed PDF — with all in-viewer annotations and form fills baked in via the existing getAnnotatedPdfBytes() path — as an embedded application/pdf resource, plus a text block with the file name, size, and whether it includes unsaved edits.
• get_current_pdf interact action (server-mediated): same result shape through the existing request-response bridge — interact enqueues a get_current_pdf command, the viewer builds the bytes and posts them back through the new app-only submit_current_pdf tool (base64 + file name + edit status), and the blocking interact call returns the text summary + embedded resource. In a commands batch, the embedded resource is kept as the command's 1:1 content slot; a single-action call keeps both parts.
• HTTP body limit raised (jsonLimit: "64mb"): express's default 100 kB JSON limit rejected the viewer's multi-MB submits. This was latent for submit_save_data and screenshot-bearing submit_page_data as well.
• Accurate "edited" detection: the Download button named a pristine document <title> - edited.pdf whenever the PDF had native annotations or form values, because annotationMap/formFieldValues are seeded with baseline state. The new hasInViewerEdits() mirrors the diff getAnnotatedPdfBytes actually applies and is shared by the Download path and both tool surfaces.
• README: documents the viewer's app tools (previously only discoverable in code) and the dual-surface export.
• Tests:
  • Unit: full interact round-trip (enqueue → poll → submit → embedded resource), viewer-error propagation, unknown-requestId guard.
  • E2E (app tool): first direct coverage of a view-registered tool — the test plays the host, posting tools/list/tools/call JSON-RPC into the app iframe from the sandbox frame; asserts a pristine %PDF export (not marked edited), then adds an annotation and asserts the re-export differs and is marked edited.
  • E2E (interact): drives the server-mediated path through the basic-host UI and asserts the same embedded-resource result.

Testing

• bun test src examples — 443 tests, 0 fail
• npx tsc -p examples/pdf-server/tsconfig.json --noEmit and tsconfig.server.json — clean
• npx playwright test tests/e2e/pdf-get-current-pdf.spec.ts — 2 passed (app-tool path exports the ~1.9 MB arXiv PDF and round-trips an annotation; interact path returns the same resource through the bridge)
• npx playwright test tests/e2e/pdf-annotations.spec.ts tests/e2e/pdf-viewer-zoom.spec.ts tests/e2e/pdf-incremental-load.spec.ts — all pass

Notes

• Both surfaces embed the whole document as base64; the tool/action descriptions tell the model to prefer a single call once editing is done. No size cap is enforced (the download path has none either) — happy to add one if preferred.
• The resource uri is file:///<URI-encoded file name> for consistency with the Download path's downloadFile payload.

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