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Attach screenshots (CDP) + ESM build fix + idempotent claim - #37
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…ild fix browser_attach_screenshot writes a PNG of the agent tab for research evidence, implemented over CDP Page.captureScreenshot (page pixels — no coordinate math, no focus steal, no other windows). Threaded through the daemon protocol/client/ surface so it works on the IPC lane too. The JXA lane's screencapture fallback is present but DISABLED by default: its -R crop works in display points while Chrome bounds + Retina scale disagree, so the region drifted onto neighbouring windows in live testing — unacceptable for an evidence file. Opt in with WUNDERLAND_ATTACH_JXA_SHOTS=1 only. Also fixes two real defects found while proving this live: - JxaBackend.claimAgentTab is now idempotent: probeIdentity() claims a tab first, so the controller's own claim consumed a SECOND about:blank and failed NO_BLANK_TAB on every attach. - package/tsconfig emit ESM (type: module, Node16) matching sibling curated extensions; the CommonJS emit made every dist import fail at runtime.
Reviewer's GuideImplements a CDP-based screenshot capture pipeline for the browser-automation attach system, fixes idempotency of tab claiming in the JXA backend, and converts the package to a proper ESM/Node16 build configuration with protocol and test updates. Sequence diagram for CDP-based browser_attach_screenshot pipelinesequenceDiagram
actor Agent
participant AttachScreenshotTool
participant AttachSurface as DaemonAttachSurface
participant DaemonClient as AttachDaemonClient
participant Daemon as AttachDaemon
participant Controller as AttachController
participant Backend as RawCdpBackend
Agent->>AttachScreenshotTool: execute({ path, fullPage })
AttachScreenshotTool->>AttachSurface: screenshot(path, fullPage)
AttachSurface->>DaemonClient: screenshot(path, fullPage)
DaemonClient->>Daemon: request('screenshot', { path, fullPage })
Daemon->>Controller: screenshot(a.path, a.fullPage)
Controller->>Backend: screenshotTab(tab, fullPage)
Backend->>Backend: send('Page.captureScreenshot', { format: 'png', captureBeyondViewport })
Backend-->>Controller: base64 PNG data
Controller->>Controller: writeFileSync(filePath, buf)
Controller-->>Daemon: { path, bytes }
Daemon-->>DaemonClient: { path, bytes }
DaemonClient-->>AttachSurface: { path, bytes }
AttachSurface-->>AttachScreenshotTool: { path, bytes }
AttachScreenshotTool-->>Agent: tool envelope with result
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📝 Walkthrough
Merge Risk: 🔵 Low · up to The screenshot feature is mergeable with awareness of a narrow local directory-swap risk. The attach documentation should also be updated to list the new tool and operation. Pre-merge checks |
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| Check name | Status | Explanation |
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Check skipped - CodeRabbit’s high-level summary is enabled. |
| Title check | |
The title clearly identifies the main screenshot feature and idempotent claim change. The referenced ESM build fix is not represented in the listed changes, but the title remains substantially related… |
| Docstring Coverage | |
Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 6 functions across 9 files. (2 skipped: 2 … |
| Linked Issues check | |
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| Out of Scope Changes check | |
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Hey - I've found 2 issues, and left some high level feedback:
- The
AttachBackend.screenshotTaband related surface/tool docs describe the capability as CDP-only and non-focusing, but the JXA backend now implementsscreenshotTaband explicitly focuses the window; consider reconciling these comments with the actual behavior or scoping the JXA implementation differently. - In the daemon
screenshothandler, invalid or missingpathcurrently returns anUNKNOWNerror code; using a more specific validation-style code (e.g., something akin toBAD_REQUEST/INVALID_ARG) would make error handling and diagnostics clearer.
Prompt for AI Agents
Please address the comments from this code review:
## Overall Comments
- The `AttachBackend.screenshotTab` and related surface/tool docs describe the capability as CDP-only and non-focusing, but the JXA backend now implements `screenshotTab` and explicitly focuses the window; consider reconciling these comments with the actual behavior or scoping the JXA implementation differently.
- In the daemon `screenshot` handler, invalid or missing `path` currently returns an `UNKNOWN` error code; using a more specific validation-style code (e.g., something akin to `BAD_REQUEST`/`INVALID_ARG`) would make error handling and diagnostics clearer.
## Individual Comments
### Comment 1
<location path="registry/curated/system/browser-automation/src/attach/backends/jxa.ts" line_range="221-230" />
<code_context>
+ const file = join(mkdtempSync(join(tmpdir(), 'attach-shot-')), 'shot.png');
</code_context>
<issue_to_address>
**suggestion (performance):** Temporary directories created for screenshots are never removed, which can accumulate over time.
Each screenshot call creates a new temp directory via `mkdtempSync`, but only `shot.png` is deleted, leaving the directory in `/tmp`. Over many runs this can lead to unnecessary disk usage, especially for long-lived processes. Please also remove the temp directory returned by `mkdtempSync` (e.g. `rmSync(dir, { recursive: true, force: true })`) in the `finally` block.
Suggested implementation:
```typescript
const { mkdtempSync, readFileSync, existsSync, rmSync } = await import('node:fs');
const { tmpdir } = await import('node:os');
const dir = mkdtempSync(join(tmpdir(), 'attach-shot-'));
const file = join(dir, 'shot.png');
```
You’ll also need to update the surrounding error-handling/cleanup logic:
1. In the `finally` block that currently deletes `shot.png` (if present), add `rmSync(dir, { recursive: true, force: true });` to remove the temporary directory.
2. If there is no `finally` block yet, wrap the screenshot capture and file reading logic in a `try`/`finally` and in `finally`:
- Check `existsSync(file)` and delete it as currently done.
- Call `rmSync(dir, { recursive: true, force: true });` to ensure the temp directory is removed even if the file was never written.
3. Ensure `dir` is in scope for that `finally` block (i.e. declared in the same function scope rather than inside a narrower block).
</issue_to_address>
### Comment 2
<location path="registry/curated/system/browser-automation/src/attach/tools.ts" line_range="118-122" />
<code_context>
+ 'Capture a PNG screenshot of the agent tab to a local file path — visual evidence for a research report. Requires the CDP transport (the AppleScript/JXA transport has no pixel access and refuses with UNSUPPORTED_OP). Read-only: never navigates or mutates the page.';
+ readonly category = 'browser';
+ readonly version = '0.1.0';
+ readonly hasSideEffects = false;
+ readonly inputSchema = {
+ type: 'object' as const,
</code_context>
<issue_to_address>
**suggestion (bug_risk):** The screenshot tool writes a file to disk, which is a side effect despite being read-only from the page’s perspective.
Although the operation is read-only for page state, `browser_attach_screenshot` still writes a PNG to disk. If `hasSideEffects` is meant to capture any external state changes (not just page mutations), this should be `true` or the semantics of `hasSideEffects` should be clarified to avoid upstream tools misclassifying this call as purely observational.
```suggestion
readonly description =
'Capture a PNG screenshot of the agent tab to a local file path — visual evidence for a research report. Requires the CDP transport (the AppleScript/JXA transport has no pixel access and refuses with UNSUPPORTED_OP). Read-only with respect to page state (never navigates or mutates the page), but writes a PNG file to disk.';
readonly category = 'browser';
readonly version = '0.1.0';
readonly hasSideEffects = true;
```
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Actionable comments posted: 4
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Inline comments:
In `@registry/curated/system/browser-automation/src/attach/AttachController.ts`:
- Around line 287-302: Constrain the file-writing logic in screenshot to a
configured evidence directory before creating the output: reject traversal,
symlinked paths, special files, and existing non-regular targets, and create the
result exclusively and atomically. Preserve dry-run behavior and return the
resolved safe destination and byte count after writing.
In `@registry/curated/system/browser-automation/src/attach/backends/jxa.ts`:
- Around line 203-245: Remove the WUNDERLAND_ATTACH_JXA_SHOTS opt-in escape
hatch from screenshotTab so the JXA screenshot implementation always rejects the
operation. Keep the existing AttachError response and do not execute raise,
bounds resolution, or screencapture while this unsafe fallback remains
unavailable.
In `@registry/curated/system/browser-automation/src/attach/backends/raw-cdp.ts`:
- Around line 215-221: Update screenshotTab to cap full-page capture dimensions
before calling Page.captureScreenshot, using the page layout or pixel bounds to
prevent oversized PNG responses. Preserve normal viewport screenshots, and
ensure the cap is applied before the base64 result is held or converted to a
Buffer.
In `@registry/curated/system/browser-automation/src/attach/tools.ts`:
- Around line 119-122: Update the screenshot tool’s hasSideEffects property to
indicate that capturing a screenshot is side-effecting because it creates
directories and writes a PNG file. Keep the existing category and version
unchanged so confirmation and policy controls apply to this tool’s local
filesystem writes.
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📒 Files selected for processing (12)
registry/curated/system/browser-automation/package.jsonregistry/curated/system/browser-automation/src/attach/AttachController.tsregistry/curated/system/browser-automation/src/attach/__tests__/pack-registration.test.tsregistry/curated/system/browser-automation/src/attach/__tests__/tools.test.tsregistry/curated/system/browser-automation/src/attach/backends/jxa.tsregistry/curated/system/browser-automation/src/attach/backends/raw-cdp.tsregistry/curated/system/browser-automation/src/attach/daemon/client.tsregistry/curated/system/browser-automation/src/attach/daemon/daemon.tsregistry/curated/system/browser-automation/src/attach/daemon/protocol.tsregistry/curated/system/browser-automation/src/attach/daemon/surface.tsregistry/curated/system/browser-automation/src/attach/tools.tsregistry/curated/system/browser-automation/tsconfig.json
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This needs six changes before it merges. The first three are security fixes.
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# Conflicts: # registry/curated/system/browser-automation/tsconfig.json
…nce directory, and the tool has side effects The six changes asked for on this pull request. browser_attach_screenshot has side effects, since it writes a file, so a deny-side-effects policy gates it. AttachController.screenshot resolves its path inside the evidence directory (~/.wunderland/attach-evidence, WUNDERLAND_ATTACH_EVIDENCE_DIR, or the evidenceDir option) and refuses a path that leaves it, passes through a link or names a file that exists, before anything is captured; the file is created with flag wx and the result gives the path written. A refused path leaves the session ready. JxaBackend.screenshotTab, its WUNDERLAND_ATTACH_JXA_SHOTS opt-in and the driver's raise command are removed: the crop drifted onto neighbouring windows. A full-page capture over CDP carries a clip of the page's CSS content size, each side cut at 16,384 px, where the whole page was captured and held in memory twice. The branch takes master's ESM tsconfig, and a changeset releases the pack as a minor.
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The six changes are in
The README has a Screenshots section and the new variable. |
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Actionable comments posted: 1
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Inline comments:
Review comments at @registry/curated/system/browser-automation/README.md:
- Line 62: Update the tool count in the README from 6 to 7 to include
browser_attach_screenshot. Check the daemon protocol for a screenshot operation
and, only if it exposes one, add that operation to the Ops list.
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.changeset/browser-automation-attach-screenshot.mdregistry/curated/system/browser-automation/README.mdregistry/curated/system/browser-automation/src/attach/AttachController.tsregistry/curated/system/browser-automation/src/attach/__tests__/AttachController.test.tsregistry/curated/system/browser-automation/src/attach/__tests__/tools.test.tsregistry/curated/system/browser-automation/src/attach/backends/__tests__/raw-cdp.test.tsregistry/curated/system/browser-automation/src/attach/backends/jxa.tsregistry/curated/system/browser-automation/src/attach/backends/raw-cdp.tsregistry/curated/system/browser-automation/src/attach/daemon/daemon-main.tsregistry/curated/system/browser-automation/src/attach/tools.tsregistry/curated/system/browser-automation/src/index.ts
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…nce directory through the write The path was checked before the capture and written after it with one writeFile, so a directory swapped for a link in between received the image. The checks move to evidence.ts and are made twice. Before the capture the evidence directory and each directory to the file must be a directory this user owns that no one else can write, under directories no other user can change (a sticky one such as /tmp is fine), as the media packs require of the files they save. After it the directories are compared by device and inode, the file is created with flag wx, and with it open the directories are compared again and the file must be the one at its path, with no other name; only then is the image written, through the handle. A write that fails removes its file. The session is reserved before the first await, so a goto or read called while the path is prepared is refused; a refused path restores it to ready, and the file is written before it is released. A session detached during the capture writes nothing. A directory that cannot take a new file is refused before the page is captured. An absolute path may name the evidence directory as configured or by its real path, which is what a written screenshot returns. The daemon client awaited a screenshot for a fixed minute. It awaits it for its own opTimeoutMs plus a margin for the file.
…wn file, and a close error fails the call After a write failed, the file was unlinked by its path alone, so a file that had taken that path meanwhile was the one removed. The bytes are now dropped through the handle, and the file is unlinked only when the path still reaches it: the same device and inode, one link, in the directories as they were checked. The handle's close was awaited with its error dropped. A file system that reports a failed write only at close (NFS, a quota) made the call return a path for an image that was not saved. The close after the write is awaited and its error fails the call. The README counts seven attach tools and lists the screenshot op.
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Two more commits after a review of
Tests: the swap during a capture, the reservation, a detach during a capture, directories others can write, a directory that cannot take a file, a failing write with and without another file at the path, a screenshot through the daemon queue, and the client's timeout. CI is green on |
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Adds
browser_attach_screenshotover CDPPage.captureScreenshot(threaded through the daemon protocol/client/surface). The JXA display-capture fallback is deliberately disabled by default — its crop drifted onto neighbouring windows in live testing, which would leak private windows into evidence files; CDP is the correct page-pixel path.Two real defects found while proving it live:
claimAgentTabwas not idempotent → every attach failedNO_BLANK_TAB(probeIdentity already claimed the tab).type: module+ Node16, matching sibling curated exts.Summary by Sourcery
Add secure CDP screenshot evidence capture to browser attachment while fixing idempotent tab claims and ESM package output.
New Features:
browser_attach_screenshottool for capturing viewport or bounded full-page PNG evidence into a protected evidence directory.Bug Fixes:
Enhancements:
Build:
Documentation:
Tests:
Summary by CodeRabbit