fix(pdf-server): viewer liveness, 1:1 batch results, fullscreen jitter

[ochafik]

What was breaking

45s hangs on get_screenshot/get_text. When the iframe never reaches startPolling() — host goes idle before mount finishes — interact waited the full GET_PAGES_TIMEOUT_MS for a viewer that isn't there, then returned a generic timeout with no hint why.

Batch errors swallowed. LocalAgentMode SDK collapses isError:true results to a bare string of content[0].text. A [fill_form, get_screenshot] batch where the screenshot timed out returned a 3-item content array, but the model only saw content[0] — which after the original ordering fix was the "Batch failed at step 2/2 (get_screenshot):" prefix with nothing after the colon. The actual error was in content[1], dropped.

Fullscreen iframe shrinking to ~85px. requestFitToContent() reads cached currentDisplayMode which defaults to "inline" and only updates if (ctx.displayMode) — if the host omits the field or the update lands one tick late, the function measures a near-empty pageWrapper and sends toolbar-height-only. Workaround was exit + re-enter fullscreen.

Fixes

server.ts

ensureViewerIsPolling() — viewsPolled Set tracks which UUIDs have polled at least once. Called before waitForPageData() in get_screenshot/get_text. Throws after 8s with a "Viewer never connected... call display_pdf again" hint if no poll arrives. Stateless polling loop on viewsPolled.has() — doesn't touch pollWaiters (would race the batch-wait branch and concurrent interact calls).

1:1 batch result contract — content[i] is the result of commands[i]. If a step fails, the batch stops there and that slot's text starts with ERROR; content.length tells the model how far it got. Multi-step batches don't set isError (the SDK's flatten would eat any prior images); single-command failures still set it since there's nothing before content[0] to lose. Tool description documents this.

console.error("[interact] ... failed after Xms") — only on failure. Goes to stderr → mcp-server-*.log, which previously had zero trace of SDK-proxied tool calls.

mcp-app.ts

Per-def try/catch in add_annotations/update_annotations — a throw on one def used to kill the whole processCommands batch including any get_pages later in the queue, so submit_page_data never fired and the server waited the full 45s.

log.error when update_annotations skips a missing id — was if (!existing) continue with no trace.

requestFitToContent reads app.getHostContext().displayMode directly — and refuses to send when pageWrapperHeight < toolbarHeight (never a real layout, just an early render).

Existing fixes from earlier on this branch (poll-on-load-error, .catch() on app.connect()) unchanged.

Tests

server.test.ts:

• get_screenshot fails fast when viewer never polled — verifies <15s + recovery hint
• get_screenshot waits full timeout when viewer polled then went silent — distinguishes never-mounted from hung-render
• get_screenshot succeeds when viewer polls during grace window — late-arriving viewer still works
• batch step failure: 1:1 content, no isError, ERROR-prefixed slot — 3-command batch where step 2 fails: content.length === 2, slot 0 untouched, slot 1 starts with ERROR, no isError

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commit: 94e31d0