refactor: replace ecosystem if-chains with IEcosystemAdapter registry

[rajbos]

Summary

Replaces the repeated ecosystem if-statement chains in extension.ts, usageAnalysis.ts, and cli/src/helpers.ts with a unified IEcosystemAdapter registry pattern.

Problem

Every method that touched session files had a chain like:

if (this.openCode.isOpenCodeSessionFile(f)) { return this.openCode.countOpenCodeInteractions(f); }
if (this.visualStudio.isVSSessionFile(f)) { ... }
if (this.crush.isCrushSessionFile(f)) { return this.crush.countCrushInteractions(f); }
// ... 4 more ecosystems

This existed in 8+ methods across 3 files. Adding a new ecosystem required updating all of them.

Solution

Adapter pattern — a common IEcosystemAdapter interface with 7 thin implementations:

interface IEcosystemAdapter {
  readonly id: string;
  readonly displayName: string;
  handles(sessionFile: string): boolean;
  stat(sessionFile: string): Promise<fs.Stats>;
  getTokens(sessionFile: string): Promise<{ tokens, thinkingTokens, actualTokens }>;
  countInteractions(sessionFile: string): Promise<number>;
  getModelUsage(sessionFile: string): Promise<ModelUsage>;
  getMeta(sessionFile: string): Promise<{ title, firstInteraction, lastInteraction, workspacePath? }>;
  getEditorRoot(sessionFile: string): string;
}

All 8 if-chain methods are replaced with:

const eco = this.findEcosystem(sessionFile);
if (eco) return eco.countInteractions(sessionFile);
// Copilot Chat fallthrough (unchanged)

Files Changed

New:

• vscode-extension/src/ecosystemAdapter.ts — IEcosystemAdapter interface
• vscode-extension/src/adapters/ — 7 adapter implementations (OpenCode, Crush, Continue, ClaudeDesktop, ClaudeCode, VisualStudio, MistralVibe)

Modified:

• vscode-extension/src/extension.ts — 8 if-chain methods replaced; findEcosystem() added
• vscode-extension/src/usageAnalysis.ts — adapter dispatch in getModelUsageFromSession() with legacy fallback
• cli/src/helpers.ts — adapter registry wired into statSessionFile(), processSessionFile(), and calculateUsageAnalysisStats()

Bugs Fixed Along the Way

• Duplicate VS check in statSessionFile() and estimateTokensFromSession() (unreachable dead code)
• Missing MistralVibe in isSpecialSession check and getSessionFileDetails()
• Missing ClaudeCode in getSessionFileDetails()

What's NOT Changed

• Copilot Chat fallthrough logic (still in-line — a future CopilotChatAdapter can wrap it)
• analyzeSessionUsage() in usageAnalysis.ts (too complex, deferred to follow-up)
• Existing DA classes are not modified — adapters are thin wrappers

Adding a New Ecosystem (Going Forward)

1. Create src/adapters/newEditorAdapter.ts implementing IEcosystemAdapter
2. Add it to the registry in the extension.ts constructor and cli/src/helpers.ts
3. Done ✅ — no if-chain hunting required