feat(web): preview document attachments in the file viewer

[juliusmarminge]

What changed

• Clicking a sent PDF or HTML attachment opens it in the right-panel file viewer, with a separate download button next to it. Other attachments download as before.
• The attachment asset resource gains an optional disposition. A document viewer sends inline; generic attachments still download by default and the server only honors inline for application/pdf and text/html, with the same CSP HTML previews already get.
• FilePreviewPanel takes an optional attachment and hides the workspace tree, breadcrumbs, editor, and "open in browser" affordances for it. shouldShowFileExplorer is the one place that decides whether the tree shows.
• Attachment surfaces live under attachment:<id> in the right panel store so they never collide with a workspace file at a matching path, and they survive the workspace going away.

Why

Agents and users share PDFs and HTML reports as attachments all the time, and until now the only thing you could do with one was download it. Workspace files already preview in place; attachments should too.

Split out of #9253, which stays a refactor.

Testing

• rightPanelStore.test.ts, MessagesTimeline.test.tsx, FilePreviewPanel.test.ts (web)
• AssetAccess.test.ts, http.test.ts (server)
• Web, server, and contracts typecheck; lint and format on changed files

Created with Claude Fable 5 using the Claude Code harness in T3 Code.

🤖 Generated with Claude Code

---

Note

Medium Risk
Changes attachment serving and inline HTML/PDF headers (security-sensitive), but extension checks and existing HTML sandboxing limit exposure; mostly UI and signed-URL claim logic.

Overview
PDF and HTML chat attachments can be opened in the right-panel file viewer on web/desktop, with a separate download control. Other file types still download when clicked.

The attachment asset contract adds optional disposition (inline / attachment). The preview panel requests inline; the server only honors it when the attachment id’s stored extension is pdf, html, or htm—not the client-supplied MIME type—so a zip cannot be forced inline. Inline PDF/HTML responses get the same Content-Type and HTML CSP behavior as workspace document previews; non-document inline requests stay download-forced.

Right panel gains openAttachment and attachment:<id> surfaces (disjoint from workspace file: tabs). Attachment previews work without an active workspace and survive workspace reconciliation. FilePreviewPanel accepts an optional attachment, loads a signed URL in a shared document iframe, and shouldShowFileExplorer hides the tree for attachments and host paths.

Messages timeline shows preview + download for browser-preview attachments (isBrowserPreviewAttachment) instead of a single download link.

^{Reviewed by Cursor Bugbot for commit 807c0fe. Bugbot is set up for automated code reviews on this repo. Configure here.}

[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	13.4 KiB	13.3 KiB	−148 B (−1.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	+3 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.4 KiB	−151 B (−2.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	55.6 KiB	−1.4 KiB (−2.5%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	13.3 KiB	13.5 KiB	+204 B (+1.5%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−1 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.6 KiB	+205 B (+3.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	56.3 KiB	57.8 KiB	+1.5 KiB (+2.7%)	66.4 KiB	✅
Claude	Live turn messages	8	10	+2 (+25.0%)	21	✅

Baseline: dbc7bfa · PR result: 807c0fe · 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: 109.4 KiB
• Claude decoded thread snapshot: 110.1 KiB

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

[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

^{Bugbot Autofix is ON, but a cloud agent failed to start.}

^{Reviewed by Cursor Bugbot for commit d3f0821. Configure here.}

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This cross-layer feature changes the default handling of PDF/HTML attachments and adds inline document serving with browser iframe execution and new right-panel state. It also broadens an existing lint suppression while moving the PDF/HTML security boundary, so the runtime and review-policy implications require human review.

Not approved because:

• Monthly spending limit reached (workspace setting). Approvability relies on correctness review in order to determine eligibility

^{Review your spending limits in Billing settings. You can add or adjust custom eligibility rules. Learn more.}

[juliusmarminge]

What changed

• Clicking a sent PDF or HTML attachment opens it in the right-panel file viewer, with a separate download button next to it. Other attachments download as before.
• The attachment asset resource gains an optional disposition. A document viewer sends inline; generic attachments still download by default and the server only honors inline for application/pdf and text/html, with the same CSP HTML previews already get.
• FilePreviewPanel takes an optional attachment and hides the workspace tree, breadcrumbs, editor, and "open in browser" affordances for it. shouldShowFileExplorer is the one place that decides whether the tree shows.
• Attachment surfaces live under attachment:<id> in the right panel store so they never collide with a workspace file at a matching path, and they survive the workspace going away.

Why

Agents and users share PDFs and HTML reports as attachments all the time, and until now the only thing you could do with one was download it. Workspace files already preview in place; attachments should too.

Split out of #9253, which stays a refactor.

Testing

• rightPanelStore.test.ts, MessagesTimeline.test.tsx, FilePreviewPanel.test.ts (web)
• AssetAccess.test.ts, http.test.ts (server)
• Web, server, and contracts typecheck; lint and format on changed files

Created with Claude Fable 5 using the Claude Code harness in T3 Code.

🤖 Generated with Claude Code

---

Note

Medium Risk
Changes attachment serving and inline HTML/PDF headers (security-sensitive), but extension checks and existing HTML sandboxing limit exposure; mostly UI and signed-URL claim logic.

Overview
PDF and HTML chat attachments can be opened in the right-panel file viewer on web/desktop, with a separate download control. Other file types still download when clicked.

The attachment asset contract adds optional disposition (inline / attachment). The preview panel requests inline; the server only honors it when the attachment id’s stored extension is pdf, html, or htm—not the client-supplied MIME type—so a zip cannot be forced inline. Inline PDF/HTML responses get the same Content-Type and HTML CSP behavior as workspace document previews; non-document inline requests stay download-forced.

Right panel gains openAttachment and attachment:<id> surfaces (disjoint from workspace file: tabs). Attachment previews work without an active workspace and survive workspace reconciliation. FilePreviewPanel accepts an optional attachment, loads a signed URL in a shared document iframe, and shouldShowFileExplorer hides the tree for attachments and host paths.

Messages timeline shows preview + download for browser-preview attachments (isBrowserPreviewAttachment) instead of a single download link.

^{Reviewed by Cursor Bugbot for commit 807c0fe. Bugbot is set up for automated code reviews on this repo. Configure here.}

[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	13.4 KiB	13.3 KiB	−148 B (−1.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	+3 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.4 KiB	−151 B (−2.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	55.6 KiB	−1.4 KiB (−2.5%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	13.3 KiB	13.5 KiB	+204 B (+1.5%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−1 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.6 KiB	+205 B (+3.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	56.3 KiB	57.8 KiB	+1.5 KiB (+2.7%)	66.4 KiB	✅
Claude	Live turn messages	8	10	+2 (+25.0%)	21	✅

Baseline: dbc7bfa · PR result: 807c0fe · 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: 109.4 KiB
• Claude decoded thread snapshot: 110.1 KiB

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

[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

^{Bugbot Autofix is ON, but a cloud agent failed to start.}

^{Reviewed by Cursor Bugbot for commit d3f0821. Configure here.}

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This cross-layer feature changes the default handling of PDF/HTML attachments and adds inline document serving with browser iframe execution and new right-panel state. It also broadens an existing lint suppression while moving the PDF/HTML security boundary, so the runtime and review-policy implications require human review.

Not approved because:

• Monthly spending limit reached (workspace setting). Approvability relies on correctness review in order to determine eligibility

^{Review your spending limits in Billing settings. You can add or adjust custom eligibility rules. Learn more.}

[juliusmarminge]

What changed

• Clicking a sent PDF or HTML attachment opens it in the right-panel file viewer, with a separate download button next to it. Other attachments download as before.
• The attachment asset resource gains an optional disposition. A document viewer sends inline; generic attachments still download by default and the server only honors inline for application/pdf and text/html, with the same CSP HTML previews already get.
• FilePreviewPanel takes an optional attachment and hides the workspace tree, breadcrumbs, editor, and "open in browser" affordances for it. shouldShowFileExplorer is the one place that decides whether the tree shows.
• Attachment surfaces live under attachment:<id> in the right panel store so they never collide with a workspace file at a matching path, and they survive the workspace going away.

Why

Agents and users share PDFs and HTML reports as attachments all the time, and until now the only thing you could do with one was download it. Workspace files already preview in place; attachments should too.

Split out of #9253, which stays a refactor.

Testing

• rightPanelStore.test.ts, MessagesTimeline.test.tsx, FilePreviewPanel.test.ts (web)
• AssetAccess.test.ts, http.test.ts (server)
• Web, server, and contracts typecheck; lint and format on changed files

Created with Claude Fable 5 using the Claude Code harness in T3 Code.

🤖 Generated with Claude Code

---

Note

Medium Risk
Changes attachment serving and inline HTML/PDF headers (security-sensitive), but extension checks and existing HTML sandboxing limit exposure; mostly UI and signed-URL claim logic.

Overview
PDF and HTML chat attachments can be opened in the right-panel file viewer on web/desktop, with a separate download control. Other file types still download when clicked.

The attachment asset contract adds optional disposition (inline / attachment). The preview panel requests inline; the server only honors it when the attachment id’s stored extension is pdf, html, or htm—not the client-supplied MIME type—so a zip cannot be forced inline. Inline PDF/HTML responses get the same Content-Type and HTML CSP behavior as workspace document previews; non-document inline requests stay download-forced.

Right panel gains openAttachment and attachment:<id> surfaces (disjoint from workspace file: tabs). Attachment previews work without an active workspace and survive workspace reconciliation. FilePreviewPanel accepts an optional attachment, loads a signed URL in a shared document iframe, and shouldShowFileExplorer hides the tree for attachments and host paths.

Messages timeline shows preview + download for browser-preview attachments (isBrowserPreviewAttachment) instead of a single download link.

^{Reviewed by Cursor Bugbot for commit 807c0fe. Bugbot is set up for automated code reviews on this repo. Configure here.}

[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	13.4 KiB	13.3 KiB	−148 B (−1.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	+3 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.4 KiB	−151 B (−2.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	55.6 KiB	−1.4 KiB (−2.5%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	13.3 KiB	13.5 KiB	+204 B (+1.5%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−1 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.6 KiB	+205 B (+3.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	56.3 KiB	57.8 KiB	+1.5 KiB (+2.7%)	66.4 KiB	✅
Claude	Live turn messages	8	10	+2 (+25.0%)	21	✅

Baseline: dbc7bfa · PR result: 807c0fe · 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: 109.4 KiB
• Claude decoded thread snapshot: 110.1 KiB

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

[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

^{Bugbot Autofix is ON, but a cloud agent failed to start.}

^{Reviewed by Cursor Bugbot for commit d3f0821. Configure here.}

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This cross-layer feature changes the default handling of PDF/HTML attachments and adds inline document serving with browser iframe execution and new right-panel state. It also broadens an existing lint suppression while moving the PDF/HTML security boundary, so the runtime and review-policy implications require human review.

Not approved because:

• Monthly spending limit reached (workspace setting). Approvability relies on correctness review in order to determine eligibility

^{Review your spending limits in Billing settings. You can add or adjust custom eligibility rules. Learn more.}

[juliusmarminge]

What changed

• Clicking a sent PDF or HTML attachment opens it in the right-panel file viewer, with a separate download button next to it. Other attachments download as before.
• The attachment asset resource gains an optional disposition. A document viewer sends inline; generic attachments still download by default and the server only honors inline for application/pdf and text/html, with the same CSP HTML previews already get.
• FilePreviewPanel takes an optional attachment and hides the workspace tree, breadcrumbs, editor, and "open in browser" affordances for it. shouldShowFileExplorer is the one place that decides whether the tree shows.
• Attachment surfaces live under attachment:<id> in the right panel store so they never collide with a workspace file at a matching path, and they survive the workspace going away.

Why

Agents and users share PDFs and HTML reports as attachments all the time, and until now the only thing you could do with one was download it. Workspace files already preview in place; attachments should too.

Split out of #9253, which stays a refactor.

Testing

• rightPanelStore.test.ts, MessagesTimeline.test.tsx, FilePreviewPanel.test.ts (web)
• AssetAccess.test.ts, http.test.ts (server)
• Web, server, and contracts typecheck; lint and format on changed files

Created with Claude Fable 5 using the Claude Code harness in T3 Code.

🤖 Generated with Claude Code

---

Note

Medium Risk
Changes attachment serving and inline HTML/PDF headers (security-sensitive), but extension checks and existing HTML sandboxing limit exposure; mostly UI and signed-URL claim logic.

Overview
PDF and HTML chat attachments can be opened in the right-panel file viewer on web/desktop, with a separate download control. Other file types still download when clicked.

The attachment asset contract adds optional disposition (inline / attachment). The preview panel requests inline; the server only honors it when the attachment id’s stored extension is pdf, html, or htm—not the client-supplied MIME type—so a zip cannot be forced inline. Inline PDF/HTML responses get the same Content-Type and HTML CSP behavior as workspace document previews; non-document inline requests stay download-forced.

Right panel gains openAttachment and attachment:<id> surfaces (disjoint from workspace file: tabs). Attachment previews work without an active workspace and survive workspace reconciliation. FilePreviewPanel accepts an optional attachment, loads a signed URL in a shared document iframe, and shouldShowFileExplorer hides the tree for attachments and host paths.

Messages timeline shows preview + download for browser-preview attachments (isBrowserPreviewAttachment) instead of a single download link.

^{Reviewed by Cursor Bugbot for commit 807c0fe. Bugbot is set up for automated code reviews on this repo. Configure here.}

[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	13.4 KiB	13.3 KiB	−148 B (−1.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	+3 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.4 KiB	−151 B (−2.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	55.6 KiB	−1.4 KiB (−2.5%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	13.3 KiB	13.5 KiB	+204 B (+1.5%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−1 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.6 KiB	+205 B (+3.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	56.3 KiB	57.8 KiB	+1.5 KiB (+2.7%)	66.4 KiB	✅
Claude	Live turn messages	8	10	+2 (+25.0%)	21	✅

Baseline: dbc7bfa · PR result: 807c0fe · 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: 109.4 KiB
• Claude decoded thread snapshot: 110.1 KiB

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

[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

^{Bugbot Autofix is ON, but a cloud agent failed to start.}

^{Reviewed by Cursor Bugbot for commit d3f0821. Configure here.}

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This cross-layer feature changes the default handling of PDF/HTML attachments and adds inline document serving with browser iframe execution and new right-panel state. It also broadens an existing lint suppression while moving the PDF/HTML security boundary, so the runtime and review-policy implications require human review.

Not approved because:

• Monthly spending limit reached (workspace setting). Approvability relies on correctness review in order to determine eligibility

^{Review your spending limits in Billing settings. You can add or adjust custom eligibility rules. Learn more.}

[juliusmarminge]

What changed

• Clicking a sent PDF or HTML attachment opens it in the right-panel file viewer, with a separate download button next to it. Other attachments download as before.
• The attachment asset resource gains an optional disposition. A document viewer sends inline; generic attachments still download by default and the server only honors inline for application/pdf and text/html, with the same CSP HTML previews already get.
• FilePreviewPanel takes an optional attachment and hides the workspace tree, breadcrumbs, editor, and "open in browser" affordances for it. shouldShowFileExplorer is the one place that decides whether the tree shows.
• Attachment surfaces live under attachment:<id> in the right panel store so they never collide with a workspace file at a matching path, and they survive the workspace going away.

Why

Agents and users share PDFs and HTML reports as attachments all the time, and until now the only thing you could do with one was download it. Workspace files already preview in place; attachments should too.

Split out of #9253, which stays a refactor.

Testing

• rightPanelStore.test.ts, MessagesTimeline.test.tsx, FilePreviewPanel.test.ts (web)
• AssetAccess.test.ts, http.test.ts (server)
• Web, server, and contracts typecheck; lint and format on changed files

Created with Claude Fable 5 using the Claude Code harness in T3 Code.

🤖 Generated with Claude Code

---

Note

Medium Risk
Changes attachment serving and inline HTML/PDF headers (security-sensitive), but extension checks and existing HTML sandboxing limit exposure; mostly UI and signed-URL claim logic.

Overview
PDF and HTML chat attachments can be opened in the right-panel file viewer on web/desktop, with a separate download control. Other file types still download when clicked.

The attachment asset contract adds optional disposition (inline / attachment). The preview panel requests inline; the server only honors it when the attachment id’s stored extension is pdf, html, or htm—not the client-supplied MIME type—so a zip cannot be forced inline. Inline PDF/HTML responses get the same Content-Type and HTML CSP behavior as workspace document previews; non-document inline requests stay download-forced.

Right panel gains openAttachment and attachment:<id> surfaces (disjoint from workspace file: tabs). Attachment previews work without an active workspace and survive workspace reconciliation. FilePreviewPanel accepts an optional attachment, loads a signed URL in a shared document iframe, and shouldShowFileExplorer hides the tree for attachments and host paths.

Messages timeline shows preview + download for browser-preview attachments (isBrowserPreviewAttachment) instead of a single download link.

^{Reviewed by Cursor Bugbot for commit 807c0fe. Bugbot is set up for automated code reviews on this repo. Configure here.}

[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	13.4 KiB	13.3 KiB	−148 B (−1.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	+3 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.4 KiB	−151 B (−2.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	55.6 KiB	−1.4 KiB (−2.5%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	13.3 KiB	13.5 KiB	+204 B (+1.5%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−1 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.6 KiB	+205 B (+3.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	56.3 KiB	57.8 KiB	+1.5 KiB (+2.7%)	66.4 KiB	✅
Claude	Live turn messages	8	10	+2 (+25.0%)	21	✅

Baseline: dbc7bfa · PR result: 807c0fe · 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: 109.4 KiB
• Claude decoded thread snapshot: 110.1 KiB

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

[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

^{Bugbot Autofix is ON, but a cloud agent failed to start.}

^{Reviewed by Cursor Bugbot for commit d3f0821. Configure here.}

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This cross-layer feature changes the default handling of PDF/HTML attachments and adds inline document serving with browser iframe execution and new right-panel state. It also broadens an existing lint suppression while moving the PDF/HTML security boundary, so the runtime and review-policy implications require human review.

Not approved because:

• Monthly spending limit reached (workspace setting). Approvability relies on correctness review in order to determine eligibility

^{Review your spending limits in Billing settings. You can add or adjust custom eligibility rules. Learn more.}

[juliusmarminge]

What changed

• Clicking a sent PDF or HTML attachment opens it in the right-panel file viewer, with a separate download button next to it. Other attachments download as before.
• The attachment asset resource gains an optional disposition. A document viewer sends inline; generic attachments still download by default and the server only honors inline for application/pdf and text/html, with the same CSP HTML previews already get.
• FilePreviewPanel takes an optional attachment and hides the workspace tree, breadcrumbs, editor, and "open in browser" affordances for it. shouldShowFileExplorer is the one place that decides whether the tree shows.
• Attachment surfaces live under attachment:<id> in the right panel store so they never collide with a workspace file at a matching path, and they survive the workspace going away.

Why

Agents and users share PDFs and HTML reports as attachments all the time, and until now the only thing you could do with one was download it. Workspace files already preview in place; attachments should too.

Split out of #9253, which stays a refactor.

Testing

• rightPanelStore.test.ts, MessagesTimeline.test.tsx, FilePreviewPanel.test.ts (web)
• AssetAccess.test.ts, http.test.ts (server)
• Web, server, and contracts typecheck; lint and format on changed files

Created with Claude Fable 5 using the Claude Code harness in T3 Code.

🤖 Generated with Claude Code

---

Note

Medium Risk
Changes attachment serving and inline HTML/PDF headers (security-sensitive), but extension checks and existing HTML sandboxing limit exposure; mostly UI and signed-URL claim logic.

Overview
PDF and HTML chat attachments can be opened in the right-panel file viewer on web/desktop, with a separate download control. Other file types still download when clicked.

The attachment asset contract adds optional disposition (inline / attachment). The preview panel requests inline; the server only honors it when the attachment id’s stored extension is pdf, html, or htm—not the client-supplied MIME type—so a zip cannot be forced inline. Inline PDF/HTML responses get the same Content-Type and HTML CSP behavior as workspace document previews; non-document inline requests stay download-forced.

Right panel gains openAttachment and attachment:<id> surfaces (disjoint from workspace file: tabs). Attachment previews work without an active workspace and survive workspace reconciliation. FilePreviewPanel accepts an optional attachment, loads a signed URL in a shared document iframe, and shouldShowFileExplorer hides the tree for attachments and host paths.

Messages timeline shows preview + download for browser-preview attachments (isBrowserPreviewAttachment) instead of a single download link.

^{Reviewed by Cursor Bugbot for commit 807c0fe. Bugbot is set up for automated code reviews on this repo. Configure here.}

[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	13.4 KiB	13.3 KiB	−148 B (−1.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	+3 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.4 KiB	−151 B (−2.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	55.6 KiB	−1.4 KiB (−2.5%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	13.3 KiB	13.5 KiB	+204 B (+1.5%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−1 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.6 KiB	+205 B (+3.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	56.3 KiB	57.8 KiB	+1.5 KiB (+2.7%)	66.4 KiB	✅
Claude	Live turn messages	8	10	+2 (+25.0%)	21	✅

Baseline: dbc7bfa · PR result: 807c0fe · 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: 109.4 KiB
• Claude decoded thread snapshot: 110.1 KiB

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

[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

^{Bugbot Autofix is ON, but a cloud agent failed to start.}

^{Reviewed by Cursor Bugbot for commit d3f0821. Configure here.}

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This cross-layer feature changes the default handling of PDF/HTML attachments and adds inline document serving with browser iframe execution and new right-panel state. It also broadens an existing lint suppression while moving the PDF/HTML security boundary, so the runtime and review-policy implications require human review.

Not approved because:

• Monthly spending limit reached (workspace setting). Approvability relies on correctness review in order to determine eligibility

^{Review your spending limits in Billing settings. You can add or adjust custom eligibility rules. Learn more.}

[juliusmarminge]

What changed

• Clicking a sent PDF or HTML attachment opens it in the right-panel file viewer, with a separate download button next to it. Other attachments download as before.
• The attachment asset resource gains an optional disposition. A document viewer sends inline; generic attachments still download by default and the server only honors inline for application/pdf and text/html, with the same CSP HTML previews already get.
• FilePreviewPanel takes an optional attachment and hides the workspace tree, breadcrumbs, editor, and "open in browser" affordances for it. shouldShowFileExplorer is the one place that decides whether the tree shows.
• Attachment surfaces live under attachment:<id> in the right panel store so they never collide with a workspace file at a matching path, and they survive the workspace going away.

Why

Agents and users share PDFs and HTML reports as attachments all the time, and until now the only thing you could do with one was download it. Workspace files already preview in place; attachments should too.

Split out of #9253, which stays a refactor.

Testing

• rightPanelStore.test.ts, MessagesTimeline.test.tsx, FilePreviewPanel.test.ts (web)
• AssetAccess.test.ts, http.test.ts (server)
• Web, server, and contracts typecheck; lint and format on changed files

Created with Claude Fable 5 using the Claude Code harness in T3 Code.

🤖 Generated with Claude Code

---

Note

Medium Risk
Changes attachment serving and inline HTML/PDF headers (security-sensitive), but extension checks and existing HTML sandboxing limit exposure; mostly UI and signed-URL claim logic.

Overview
PDF and HTML chat attachments can be opened in the right-panel file viewer on web/desktop, with a separate download control. Other file types still download when clicked.

The attachment asset contract adds optional disposition (inline / attachment). The preview panel requests inline; the server only honors it when the attachment id’s stored extension is pdf, html, or htm—not the client-supplied MIME type—so a zip cannot be forced inline. Inline PDF/HTML responses get the same Content-Type and HTML CSP behavior as workspace document previews; non-document inline requests stay download-forced.

Right panel gains openAttachment and attachment:<id> surfaces (disjoint from workspace file: tabs). Attachment previews work without an active workspace and survive workspace reconciliation. FilePreviewPanel accepts an optional attachment, loads a signed URL in a shared document iframe, and shouldShowFileExplorer hides the tree for attachments and host paths.

Messages timeline shows preview + download for browser-preview attachments (isBrowserPreviewAttachment) instead of a single download link.

^{Reviewed by Cursor Bugbot for commit 807c0fe. Bugbot is set up for automated code reviews on this repo. Configure here.}

[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	13.4 KiB	13.3 KiB	−148 B (−1.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	+3 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.4 KiB	−151 B (−2.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	55.6 KiB	−1.4 KiB (−2.5%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	13.3 KiB	13.5 KiB	+204 B (+1.5%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−1 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.6 KiB	+205 B (+3.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	56.3 KiB	57.8 KiB	+1.5 KiB (+2.7%)	66.4 KiB	✅
Claude	Live turn messages	8	10	+2 (+25.0%)	21	✅

Baseline: dbc7bfa · PR result: 807c0fe · 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: 109.4 KiB
• Claude decoded thread snapshot: 110.1 KiB

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

[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

^{Bugbot Autofix is ON, but a cloud agent failed to start.}

^{Reviewed by Cursor Bugbot for commit d3f0821. Configure here.}

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This cross-layer feature changes the default handling of PDF/HTML attachments and adds inline document serving with browser iframe execution and new right-panel state. It also broadens an existing lint suppression while moving the PDF/HTML security boundary, so the runtime and review-policy implications require human review.

Not approved because:

• Monthly spending limit reached (workspace setting). Approvability relies on correctness review in order to determine eligibility

^{Review your spending limits in Billing settings. You can add or adjust custom eligibility rules. Learn more.}

[juliusmarminge]

What changed

• Clicking a sent PDF or HTML attachment opens it in the right-panel file viewer, with a separate download button next to it. Other attachments download as before.
• The attachment asset resource gains an optional disposition. A document viewer sends inline; generic attachments still download by default and the server only honors inline for application/pdf and text/html, with the same CSP HTML previews already get.
• FilePreviewPanel takes an optional attachment and hides the workspace tree, breadcrumbs, editor, and "open in browser" affordances for it. shouldShowFileExplorer is the one place that decides whether the tree shows.
• Attachment surfaces live under attachment:<id> in the right panel store so they never collide with a workspace file at a matching path, and they survive the workspace going away.

Why

Agents and users share PDFs and HTML reports as attachments all the time, and until now the only thing you could do with one was download it. Workspace files already preview in place; attachments should too.

Split out of #9253, which stays a refactor.

Testing

• rightPanelStore.test.ts, MessagesTimeline.test.tsx, FilePreviewPanel.test.ts (web)
• AssetAccess.test.ts, http.test.ts (server)
• Web, server, and contracts typecheck; lint and format on changed files

Created with Claude Fable 5 using the Claude Code harness in T3 Code.

🤖 Generated with Claude Code

---

Note

Medium Risk
Changes attachment serving and inline HTML/PDF headers (security-sensitive), but extension checks and existing HTML sandboxing limit exposure; mostly UI and signed-URL claim logic.

Overview
PDF and HTML chat attachments can be opened in the right-panel file viewer on web/desktop, with a separate download control. Other file types still download when clicked.

The attachment asset contract adds optional disposition (inline / attachment). The preview panel requests inline; the server only honors it when the attachment id’s stored extension is pdf, html, or htm—not the client-supplied MIME type—so a zip cannot be forced inline. Inline PDF/HTML responses get the same Content-Type and HTML CSP behavior as workspace document previews; non-document inline requests stay download-forced.

Right panel gains openAttachment and attachment:<id> surfaces (disjoint from workspace file: tabs). Attachment previews work without an active workspace and survive workspace reconciliation. FilePreviewPanel accepts an optional attachment, loads a signed URL in a shared document iframe, and shouldShowFileExplorer hides the tree for attachments and host paths.

Messages timeline shows preview + download for browser-preview attachments (isBrowserPreviewAttachment) instead of a single download link.

^{Reviewed by Cursor Bugbot for commit 807c0fe. Bugbot is set up for automated code reviews on this repo. Configure here.}

[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	13.4 KiB	13.3 KiB	−148 B (−1.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	+3 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.4 KiB	−151 B (−2.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	55.6 KiB	−1.4 KiB (−2.5%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	13.3 KiB	13.5 KiB	+204 B (+1.5%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−1 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.6 KiB	+205 B (+3.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	56.3 KiB	57.8 KiB	+1.5 KiB (+2.7%)	66.4 KiB	✅
Claude	Live turn messages	8	10	+2 (+25.0%)	21	✅

Baseline: dbc7bfa · PR result: 807c0fe · 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: 109.4 KiB
• Claude decoded thread snapshot: 110.1 KiB

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

[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

^{Bugbot Autofix is ON, but a cloud agent failed to start.}

^{Reviewed by Cursor Bugbot for commit d3f0821. Configure here.}

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This cross-layer feature changes the default handling of PDF/HTML attachments and adds inline document serving with browser iframe execution and new right-panel state. It also broadens an existing lint suppression while moving the PDF/HTML security boundary, so the runtime and review-policy implications require human review.

Not approved because:

• Monthly spending limit reached (workspace setting). Approvability relies on correctness review in order to determine eligibility

^{Review your spending limits in Billing settings. You can add or adjust custom eligibility rules. Learn more.}