fix: resolved AI/OAuth helper duplication via shared modules

- Standardized missing-file read errors and now return `File not found: <path>` for absent edit targets.
- Centralized AI provider, usage, and OAuth helpers into shared modules to remove duplicated logic.
- Migrated OAuth/API-key login flows to shared factory helpers and removed inline prompt/token-exchange code.
- Reused shared tools and formatter utilities for discovery, stream tails, LSP batching, and source formatting.
- Consolidated repeated test helpers and fixtures into shared modules, replacing inline helper duplicates.

packages/coding-agent/test/agent-storage-sqlite-compat.test.ts

@@ -4,21 +4,10 @@ import * as fs from "node:fs/promises";
 import * as os from "node:os";
 import * as path from "node:path";
 import { AgentStorage } from "../src/session/agent-storage";
+import { readTableSql } from "./helpers/sqlite-inspect";
 
 const LEGACY_TIMESTAMP = 1_700_000_000;
 
-function readTableSql(dbPath: string, tableName: string): string | null {
-	const db = new Database(dbPath, { readonly: true });
-	try {
-		const row = db.prepare("SELECT sql FROM sqlite_master WHERE type = 'table' AND name = ?").get(tableName) as
-			| { sql?: string | null }
-			| undefined;
-		return row?.sql ?? null;
-	} finally {
-		db.close();
-	}
-}
-
 function readSchemaVersion(dbPath: string): number | null {
 	const db = new Database(dbPath, { readonly: true });
 	try {