fix(editor): stabilize restored tab highlighting

[bajrangCoder]

No description provided.

[greptile-apps]

Greptile Summary

This PR stabilizes tab highlighting and header updates during file loading by moving file.tab.classList.add("active"), file.tab.scrollIntoView(), and $header updates to execute immediately on tab switch — before the editor state is applied. It also introduces a proper showLoadingEditor placeholder for unloaded files and refactors the scattered per-call-site language-extension logic into unified resolveLanguageExtension / dispatchLanguageExtension helpers.

• Tab ordering fix: UI state (tab.active, header text) is now set eagerly before applyFileToEditor/showLoadingEditor, eliminating the flash where the header showed the previous file's name.
• Loading placeholder: showLoadingEditor creates a minimal but fully compartmented EditorState (including all cmOptionSpecs compartments, languageCompartment, and lspCompartment) so any settings dispatches that fire during the load window land on compartments that actually exist in the state.
• Language lifecycle tracking: New __cmLanguageReady / __cmLanguageSignature per-file flags prevent duplicate or stale language-extension dispatches across tab switches and file reloads.

Confidence Score: 5/5

Safe to merge. The changes are well-scoped: UI state is applied eagerly before the editor swap, the loading placeholder now carries all required compartments, and the language-extension lifecycle is guarded against stale async dispatches.

No wrong-state dispatches, data loss, or broken contracts were found. The refactored helpers correctly guard async language resolves with both an activeFile id check and a signature check. The new showLoadingEditor state includes all compartments that settings-update handlers reconfigure, so no missing-compartment throws can occur during a session-restore window.

No files require special attention. The minor edge case around switch-back-during-load in editorManager.js self-heals via the file-loaded event.

Important Files Changed

Filename	Overview
src/lib/editorManager.js	Core of the PR: moves tab/header updates earlier, adds showLoadingEditor, refactors language extension management into reusable helpers, and adds options-signature caching to skip redundant applyOptions calls
src/lib/editorFile.js	Removes the early interim file-loaded emit from #loadText and resets __cmLanguageReady/__cmLanguageSignature when a file session is freshly created

Sequence Diagram

sequenceDiagram
    participant User
    participant EditorFile
    participant switchFile
    participant Editor

    User->>EditorFile: click tab (file not loaded)
    EditorFile->>switchFile: switchFile(id)
    switchFile->>switchFile: file.tab.classList.add("active")
    switchFile->>switchFile: "$header.text = file.filename"
    switchFile->>Editor: showLoadingEditor(file)
    switchFile-->>EditorFile: return
    EditorFile->>EditorFile: "#loadText() → file.loading=true"
    EditorFile->>EditorFile: await readFile / cache
    EditorFile->>EditorFile: "file.session = EditorState({doc:value})"
    EditorFile->>switchFile: emit("file-loaded", file)
    switchFile->>Editor: applyFileToEditor(file)
    Editor->>Editor: resolveLanguageExtension (sync or async)
    Note over Editor: async path guarded by activeFile.id check

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_{Reviews (2): Last reviewed commit: "fix" | Re-trigger Greptile}