fix(server): bound preview snapshot metadata

[devhims]

Problem

preview_snapshot forwards Chrome's full accessibility tree to the provider. On large pages, this can add hundreds of kilobytes of JSON to one tool result and consume most of the thread's context window.

Fix

Cap snapshot metadata at 64 KB. If it exceeds the limit, omit the accessibility tree and mark the result as truncated. If the remaining fields are still too large, return a compact page summary. Normal snapshots are unchanged.

Added a regression test that sends an oversized snapshot through the MCP tool and verifies that the returned metadata stays within the limit.

Validation

• vp test run apps/server/src/mcp/McpHttpServer.test.ts
• vp run --filter t3 typecheck
• Targeted lint and formatting checks

Implemented with GPT-5 via Codex desktop.

Note

Bound preview snapshot metadata to 64,000 bytes in preview_snapshot tool

• Adds a previewSnapshotMetadata helper in McpHttpServer.ts that serializes snapshot metadata (excluding screenshot data) and truncates it if it exceeds 64,000 bytes.
• When over the limit, it first drops accessibilityTree and marks truncation with reason metadata_size_limit; if still over, it falls back to truncating strings (visibleText to 8,000 chars, URL/title) and clearing list fields.
• The preview_snapshot handler now uses this helper for both the text content (serialized JSON) and structuredContent (bounded metadata object).
• Behavioral Change: oversized snapshot responses will now be truncated with truncation metadata rather than returned as-is.

^{Macroscope summarized 3cdc4c5.}

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[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This is a straightforward defensive fix that bounds preview snapshot metadata to 64KB with progressive truncation. The logic is clear and well-tested, but the author is a first-time contributor to this codebase, warranting human verification of the truncation approach.

^{You can add or adjust custom eligibility rules. Learn more.}

[t3dotgg]

Note

🤖 GPT-6 Astra (preview) responding on behalf of Theo

This was closed as part of an automated cleanup pass. If you believe it was closed in error, reply here and we will get it reopened.

Closing in favor of #9505, the retained snapshot-size fix. It declares truncation in the contract and keeps interactive locators longer. Its latest code also caps title and URL, so this branch adds no unique limiter behavior. Review continues there.