Case Study A — Safe TS Migration Pack

field-rename in a real codebase

Renaming config.baseUrl to config.apiBaseUrl across sovr-mcp-server — a 22-file, 2,042-line TypeScript project. Every reference found. Every patch verified. Zero manual edits.

Hits Found

Patches Generated

Files Changed

PASS

Verify Result

What was renamed

Kind	Count	Classification
Type field declaration	1	safe
Property key in object literal	1	safe
Value reference (property access)	7	safe
this.config.baseUrl chain	2	safe
Destructuring shorthand	1	safe
Template literal interpolation	1	safe

Generated Diffs

Every patch, character-precise.

Type field declaration

@src/types/index.ts

export interface Config {

- baseUrl: string;

+ apiBaseUrl: string;

apiKey: string;

timeout?: number;

}

Property key + value reference

@src/index.ts

const config: Config = {

- baseUrl: process.env.API_URL ?? "http://localhost:3000",

+ apiBaseUrl: process.env.API_URL ?? "http://localhost:3000",

apiKey: process.env.API_KEY ?? "",

};

this.config chain in class method

@src/api/client.ts

export class ApiClient {

constructor(private config: Config) {}

async request(path: string) {

- const url = `${this.config.baseUrl}${path}`;

+ const url = `${this.config.apiBaseUrl}${path}`;

return fetch(url, {

headers: this.getHeaders(),

});

}

getEndpoint() {

- return this.config.baseUrl;

+ return this.config.apiBaseUrl;

}

Destructuring shorthand expansion

@src/utils/helpers.ts

function createClient(config: Config) {

- const { baseUrl, apiKey } = config;

+ const { apiBaseUrl: baseUrl, apiKey } = config;

return new ApiClient(baseUrl, apiKey);

}

Safe-Apply Verification

tsc --noEmit on patched copy: 0 errors

Applied: yes (all 13 patches written)

Post-apply tsc: still green

In Trial #005a on a different repo (SOVR-MCP-PROXY), safe-apply correctly blocked a write when the rename left a string literal "url" in a required array inconsistent with the renamed property. A human would have shipped that bug.

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