[latekvo]

Closes #826

Over MCP, screenshot-diff returned only the downscaled context image and the summary. Both diff files were materialized locally, but their paths were never sent, even though the summary tells the agent to "see diffPath (full size) and contextDiffPath in this result". The adapter now adds diffPath: <local path> and contextDiffPath: <local path> text blocks after the summary. If an artifact could not be downloaded, its line reads (unavailable), as flow-step artifacts already do.

No docs update needed. The tool description already lists both fields among the returned fields.

Verification

The E2E runs the real built tool-server (ARGENT_TOOLS_URL, no device) and the real startMcpServer over stdio with an @modelcontextprotocol/sdk client. It calls screenshot-diff on two generated 400x800 PNGs.

Before (main):

[0] image base64Bytes=1136
[1] text: "Screenshot diff summary ... - diff_images: see diffPath (full size) and contextDiffPath in this result ..."
current-diff.png anywhere: false

After:

[0] image base64Bytes=1136
[1] text: "Screenshot diff summary ..."
[2] text: "diffPath: /var/folders/.../argent-screenshot-diff/d32dc1ea68f7/current-diff.png"
[3] text: "contextDiffPath: /var/folders/.../argent-screenshot-diff/d32dc1ea68f7/current-context-diff.png"
diffPath local exists: true dims=400x800 ; context image dims=120x240

Edge cases, covered by test/content.test.ts against the real materializer:

• full-size download fails (404): diffPath: (unavailable), and the context image and path still render
• both fields absent (dimension_mismatch): no path lines
• remote artifact handles: rewritten to downloaded local paths

Checks: tsc --build, tsc -p tsconfig.test.json, argent-mcp vitest 124/124, eslint, prettier, knip. The new tests fail 3/43 against the previous content.ts. Every mutant of the new lines tried (dropping the (unavailable) fallback, dropping contextDiffPath, dropping the absent-field skip, reading the un-materialized value) fails at least one test.

Out of scope, found while reviewing: #1574 (remote downloads with the same filename overwrite each other).

[latekvo]

[Diplomat, Opus 5.5]: Out of scope, filed separately: #1574. When the tool-server is remote, two downloaded artifacts with the same filename (for example two diffs of a current.png) land at one local path, so a diffPath this PR hands to the agent can later hold a different call's diff. Confirmed by calling materializeArtifacts twice from the built tools-client dist: same path, and the first file's bytes were replaced by the second's.

[latekvo]

Folded into #1753 as cf6f92a, to review together with the other capture fixes.