fix(web): images, video, HTML and PDF preview in a thread before its first message

[juliusmarminge]

Opening an HTML, PDF, image, video or audio file from the file tree in a new thread showed "Unable to load file preview." until the thread's first message was sent.

The preview asks the server for a signed asset URL and names the thread. A draft thread doesn't exist on the server yet, so resolving its workspace failed (ProjectionStoreThreadNotFoundError, then AssetWorkspaceContextResolutionError). The contract already has draft-workspace-file, which names the workspace root directly, and the server already serves it; the file panel just never used it.

workspaceAssetResource in filePreviewMode.ts now picks the resource: draft-workspace-file for a draft, the thread-scoped resource otherwise. All four previews use it. The panel tells a draft by its composer target, which is a DraftId until the thread exists.

Found while testing the browser preview build.

🤖 Generated with Claude Code (Opus 5.5)
Closes #17273

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[macroscopeapp]

🟡 Medium files/filePreviewMode.ts:73

Draft HTML in the workspace cannot load sibling CSS, scripts, or images because this returns its absolute path, causing the server to issue a media-file-exact claim that rejects requests for those sibling paths. Pass a workspace-relative path for in-workspace browser documents while retaining absolute paths for host files and media.

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In file @apps/web/src/components/files/filePreviewMode.ts around line 73:

Draft HTML in the workspace cannot load sibling CSS, scripts, or images because this returns its absolute path, causing the server to issue a `media-file-exact` claim that rejects requests for those sibling paths. Pass a workspace-relative path for in-workspace browser documents while retaining absolute paths for host files and media.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Path: .coderabbit.config.ts
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• Run ID: 7461d926-651a-4adf-be18-9e258a1a7804

📥 Commits

Reviewing files that changed from the base of the PR and between d81afa0 and 868030d.

📒 Files selected for processing (3)

• apps/web/src/components/files/FilePreviewPanel.test.ts
• apps/web/src/components/files/FilePreviewPanel.tsx
• apps/web/src/components/files/filePreviewMode.ts

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📝 Walkthrough

Walkthrough

Workspace preview components now build asset resources through a shared helper. The helper returns a draft workspace-file resource when the composer target is a draft. Otherwise, it uses the supplied resource kind and thread ID.

Changes

Workspace asset resources

Layer / File(s)	Summary
Draft-aware resource helper apps/web/src/components/files/filePreviewMode.ts, apps/web/src/components/files/FilePreviewPanel.test.ts	Adds workspaceAssetResource and tests its draft and non-draft resource shapes.
Workspace preview integration apps/web/src/components/files/FilePreviewPanel.tsx	Passes draft status and workspace root to preview components. The components use the helper to create resources while preserving the browser preview’s workspace-path resource-kind selection.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: maria-rcks

Merge Risk: ⚪ Minimal · up to 86803

The draft preview change appears mergeable after normal checks.

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check		The description explains the problem and implementation, and it references issue #17273. It does not provide the required Verification section with focused test results, and it does not clearly docume…	Add explicit Scope and approval and Verification sections. Document the issue or maintainer approval, or explain why this focused bug fix needs no prior approval. Describe the focused tests or manual checks performed and their observed resu…

✅ Passed checks (3 passed)

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Title check		The title clearly and concisely describes the main fix for previews in a thread before its first message. It uses the repository's conventional commit format.

Full details: Description check

Explanation

The description explains the problem and implementation, and it references issue #17273. It does not provide the required Verification section with focused test results, and it does not clearly document scope approval or why the change qualifies as an obvious bug fix. It also lacks the required UI screenshots or recording.

Resolution

Add explicit Scope and approval and Verification sections. Document the issue or maintainer approval, or explain why this focused bug fix needs no prior approval. Describe the focused tests or manual checks performed and their observed results. Include before-and-after screenshots and a short recording if interaction or timing details require them.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Codex	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Codex	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Codex	Live turn WebSocket decoded	20.9 KiB	20.9 KiB	0 B (0.0%)	29.3 KiB	✅
Codex	Live turn messages	2	2	0 (0.0%)	8	✅
Claude	Total thread wire	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Claude	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Claude	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Claude	Live turn WebSocket decoded	21.2 KiB	21.2 KiB	0 B (0.0%)	29.3 KiB	✅
Claude	Live turn messages	2	2	0 (0.0%)	8	✅

Baseline: d81afa0 · PR result: 868030d · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 108.5 KiB
• Claude decoded thread snapshot: 108.8 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[macroscopeapp]

Approvability

Verdict: Would Approve

Macroscope's review found this PR approvable — This is a focused web bug fix that routes draft previews through the existing draft workspace asset flow while leaving established thread previews unchanged. A separate Medium-severity finding identifies a remaining limitation for sibling assets in draft HTML documents.

Not approved because:

• 1 blocking correctness issue found at or above your repo's Minimum Blocking Severity

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