improvement(chat): code-split resource preview panel out of initial /chat bundle

[waleedlatif1]

Summary

• Code-split the MothershipView resource-preview panel (file-viewer, rich-markdown, CSV/PDF stack) out of the initial /chat bundle via React.lazy + a local <Suspense>. It only renders once a chat has messages, so it no longer ships on every navigation to /chat.
• Removed the now-dead barrel re-export of MothershipView so the split actually takes effect — this app has no "sideEffects": false, so a leftover barrel edge would drag the heavy module back into the initial chunk.
• Small behavior-preserving perf pass on the input surface: toSorted (non-mutating) instead of spread+sort in use-skill-auto-mention; a Map first-match lookup instead of .find()-in-loop in prompt-editor.
• Documented the code-split/barrel gotcha in .claude/rules/sim-imports.md.

Type of Change

• Improvement (performance)

Testing

• tsc 0 errors, biome clean
• user-input tests 14/14 pass
• Two independent adversarial audits confirmed zero regression: ref forwarding through lazy(memo(forwardRef)) reaches the DOM node (resize keeps working), the fallback window is null-guarded in use-mothership-resize, Suspense is scoped locally (no page-level fallback flash), and the two micro-fixes are behaviorally identical (first-match preserved, non-mutating sort)

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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Project	Deployment	Actions	Updated (UTC)
docs	Ready	Preview, Comment	Jul 1, 2026 8:11pm

[cursor]

PR Summary

Low Risk
Performance and import-structure changes with behavior-preserving mention rendering; main risk is verifying the bundle split and that resize/ref handling tolerates the lazy Suspense window (already guarded per PR notes).

Overview
Code-splits the resource preview panel (MothershipView — file viewer, rich markdown, CSV/PDF) off the initial /chat bundle by loading it with React.lazy from the deep ./components/mothership-view/mothership-view path and wrapping it in a local <Suspense fallback={null}> on home.tsx, so the heavy stack only loads when the chat-with-messages layout mounts.

Removes MothershipView from components/index.ts so the barrel no longer keeps a static edge to that module (important without "sideEffects": false in the app package). Documents this lazy + barrel pattern in .claude/rules/sim-imports.md, including local Suspense and ref null-guards during the fallback window.

Micro perf in prompt-editor: builds a label→context Map for mention overlay rendering instead of contexts.find() inside the highlight loop (first-match semantics unchanged).

^{Reviewed by Cursor Bugbot for commit 5c0f786. Configure here.}

[greptile-apps]

Greptile Summary

This PR code-splits the MothershipView resource-preview panel (file-viewer, rich-markdown, CSV/PDF stack) out of the initial /chat route bundle using React.lazy + a local <Suspense>, and removes the now-dead barrel re-export that would have silently re-pulled the heavy module back into the initial chunk.

• Lazy-load + barrel removal: home.tsx now imports MothershipView via a deep lazy(() => import('./components/mothership-view/mothership-view')) and the corresponding export { MothershipView } line is deleted from components/index.ts, ensuring no bundler edge reintroduces the chunk.
• prompt-editor.tsx micro-optimization: a Map<label, context> is built once before the range loop, replacing an O(n) .find() call per mention range with an O(1) lookup; first-match semantics are preserved.
• Documentation: .claude/rules/sim-imports.md documents the code-split/barrel interaction so the pattern is not accidentally regressed.

Confidence Score: 5/5

Safe to merge — the change is purely additive in bundle terms, all DOM ref usages remain guarded, and the barrel removal has no other consumers.

The lazy split is implemented correctly: the deep import path bypasses the barrel, the Suspense boundary is scoped locally so there is no page-level flash, and every access to mothershipRef.current in use-mothership-resize.ts already carries a null guard (if (!el) return / optional chaining). The barrel re-export removal was verified to have no remaining consumers. The Map optimization in prompt-editor preserves first-match semantics. No regressions were introduced.

No files require special attention.

Important Files Changed

Filename	Overview
apps/sim/app/workspace/[workspaceId]/home/home.tsx	Introduces React.lazy + local Suspense for MothershipView; all mothershipRef.current usages in use-mothership-resize.ts are null-guarded, so the fallback window is safe.
apps/sim/app/workspace/[workspaceId]/home/components/index.ts	Dead barrel re-export of MothershipView removed; no other file imported MothershipView from this barrel, so the change is safe.
apps/sim/app/workspace/[workspaceId]/home/components/user-input/components/prompt-editor/prompt-editor.tsx	Map built outside the range loop for O(1) mention lookups; first-match semantics preserved with has() guard before set(); only constructed when ranges exist (after early-return guards).
.claude/rules/sim-imports.md	Documents the code-split/barrel interaction, Suspense scoping, and ref null-guard requirement — accurate and helpful for preventing future regression.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant Browser
    participant Next.js
    participant InitialChunk as /chat initial chunk
    participant LazyChunk as MothershipView chunk (lazy)

    Browser->>Next.js: navigate to /chat
    Next.js->>InitialChunk: load (home.tsx, MothershipChat, UserInput, etc.)
    Note over InitialChunk: MothershipView NOT included
    InitialChunk-->>Browser: render landing view (no messages)

    Browser->>Next.js: user sends first message
    Next.js-->>Browser: "hasMessages = true, non-early-return branch"
    Browser->>LazyChunk: React.lazy triggers fetch
    LazyChunk-->>Browser: MothershipView chunk loaded
    Note over Browser: Suspense fallback=null during load (no flash)
    Browser-->>Browser: MothershipView mounts with ref forwarded

Loading

%%{init: {'theme': 'base', 'themeVariables': {"darkMode": true, "background": "#0d1117", "primaryColor": "#21262d", "primaryTextColor": "#e6edf3", "primaryBorderColor": "#8b949e", "lineColor": "#8b949e", "textColor": "#e6edf3", "edgeLabelBackground": "#161b22", "actorBkg": "#21262d", "actorBorder": "#8b949e", "actorTextColor": "#e6edf3", "actorLineColor": "#8b949e", "signalColor": "#8b949e", "signalTextColor": "#e6edf3", "noteBkgColor": "#373320", "noteBorderColor": "#d4a72c", "noteTextColor": "#f0e6c0", "labelBoxBkgColor": "#21262d", "labelBoxBorderColor": "#8b949e", "labelTextColor": "#e6edf3", "loopTextColor": "#e6edf3", "activationBkgColor": "#30363d", "activationBorderColor": "#8b949e"}}}%%
sequenceDiagram
    participant Browser
    participant Next.js
    participant InitialChunk as /chat initial chunk
    participant LazyChunk as MothershipView chunk (lazy)

    Browser->>Next.js: navigate to /chat
    Next.js->>InitialChunk: load (home.tsx, MothershipChat, UserInput, etc.)
    Note over InitialChunk: MothershipView NOT included
    InitialChunk-->>Browser: render landing view (no messages)

    Browser->>Next.js: user sends first message
    Next.js-->>Browser: "hasMessages = true, non-early-return branch"
    Browser->>LazyChunk: React.lazy triggers fetch
    LazyChunk-->>Browser: MothershipView chunk loaded
    Note over Browser: Suspense fallback=null during load (no flash)
    Browser-->>Browser: MothershipView mounts with ref forwarded

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[waleedlatif1]

@greptile

[waleedlatif1]

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^{Reviewed by Cursor Bugbot for commit 5c0f786. Configure here.}