fix(agent-runtime): keep MCP embedded resource text in tool results

[xpeng5278-web]

Summary

Fixes #1549

When an MCP tool result has a text block, the host tool bridge sent only text and image blocks to the model. It dropped resource (embedded resource) and resource_link blocks. github-mcp-server get_file_contents returns a status line plus the file body as an embedded text resource, so the agent saw "successfully downloaded text file" but not the file.

This change adds a small hostContentBlockText helper, used by both the MCP content branch and the bare content-block-array branch:

• text → its text (unchanged)
• resource with resource.text → the resource text
• resource_link → a one-line [resource link] <name>: <uri> reference
• binary resources and other kinds → still not inlined (no base64 in the text channel)

Image handling, details, and the JSON fallback for results with no text-like blocks are unchanged. Restored history already reads the normalized content, so the text survives a restart.

Tests

• New runtime.test.ts case uses the github-mcp-server response shape (status text + embedded resource + resource link). It fails on main (the model text is only the status line) and passes with this change.
• packages/agent-runtime: vitest run → 96 files / 1329 tests pass; tsc --noEmit clean.
• pnpm lint:biome, pnpm check:pr-base pass.

Docs

docs/spec/03-runtime/02-agent-runtime.md §3.3 now documents embedded text resources and resource links.

[muzimu217]

Verified locally on macOS (worktree off current main): agent-runtime full suite 96 files / 1329 tests pass, including the new embedded-resource cases.

The fix restores a real capability loss: github-mcp-server's get_file_contents returns the file body as an embedded resource block, and the host bridge was passing through only text and image blocks — so the agent saw "successfully downloaded text file" with no file. hostContentBlockText handling resource/resource_link (with the resource URI in the rendered text, so the model can cite what it read) applied on both the content branch and the bare content-block-array branch is the right minimal shape.

One nuance worth stating in the review for future readers (not blocking): a large embedded resource now lands in full in the model context, which can push long files toward the overflow path — acceptable, since #1517's classification (merged) makes that surface correctly instead of looping.

Nothing blocking. fix scope, fits the window.

[vastsa]

Confirmed that host tool normalization kept only text and image blocks, which dropped embedded text resources and resource links whenever a status line was present. The fix handles both MCP content shapes and preserves the body/link for the model. Current-main checks all pass.