P1: add affected tests command

README.md

@@ -57,11 +57,18 @@ This repo keeps test fixtures out of default Codegraph scans with `codegraph.con
 {
   "discovery": {
     "ignoreGlobs": ["tests/samples/**", "tests/languages/samples/**"]
+  },
+  "languages": {
+    "extensions": {
+      ".tpl": "php"
+    }
   }
 }
 ```
 
-Use this pattern in other repos when large fixture, generated, or vendored trees should not participate in search, unresolved-import checks, graphing, indexing, inspect, impact, or review runs. Config globs are project-root-relative. CLI `--include-glob` and `--ignore-glob` stay relative to each active scan root.
+Use discovery globs in other repos when large fixture, generated, or vendored trees should not participate in search, unresolved-import checks, graphing, indexing, inspect, impact, or review runs. Config globs are project-root-relative, while CLI `--include-glob` and `--ignore-glob` stay relative to each active scan root.
+
+`languages.extensions` maps additional or built-in literal file suffixes to supported language IDs; longer suffixes win, and built-ins remain active unless explicitly remapped. Suffixes may contain letters, digits, `.`, `_`, `+`, and `-`. The `.vue` and `.svelte` suffixes are always handled as single-file components and cannot be remapped.
 
 ## Quick start
 
@@ -87,6 +94,9 @@ node ./dist/cli.js review --base HEAD --head WORKTREE --summary
 # broader blast-radius map when the review packet needs expansion
 node ./dist/cli.js impact --base HEAD --head WORKTREE --pretty
 
+# focused affected-test list for current edits
+node ./dist/cli.js affected --base HEAD --head WORKTREE --quiet
+
 # one-call answer for a concrete repo question
 node ./dist/cli.js explore "how does auth reach db?" --root . --pretty
 
@@ -138,6 +148,7 @@ Use these as starting points, then see [docs/cli.md](./docs/cli.md) for all flag
 # fastest code-review handoff for current edits
 codegraph review --base HEAD --head WORKTREE --summary
 codegraph impact --base HEAD --head WORKTREE --pretty
+codegraph affected --base HEAD --head WORKTREE --quiet
 
 # repo question, orientation, and bounded follow-up
 codegraph explore "how does auth reach db?" --root . --pretty

codegraph-skill/codegraph/SKILL.md

@@ -9,7 +9,7 @@ Use Codegraph for structure-aware repo questions:
 
 - repo overview, hotspots, cycles, unresolved imports, and public API surface
 - symbol navigation with definitions, references, dependencies, and paths
-- PR or worktree impact review with candidate tests and risk signals
+- PR or worktree impact review with candidate tests, affected test lists, and risk signals
 - duplicate cleanup and refactor-risk triage
 - bounded agent context through explore, orientation, search, packets, explain, and MCP
 
@@ -40,6 +40,7 @@ Then choose the smallest useful follow-up:
 - references: `codegraph refs --file <file> --line <line> --col <column> --pretty`
 - duplicates: `codegraph duplicates --root . ./src --profile cleanup`
 - impact: `codegraph impact --base HEAD --head WORKTREE --pretty`
+- affected tests: `codegraph affected --base HEAD --head WORKTREE --quiet`
 - review: `codegraph review --base HEAD --head WORKTREE --summary`
 - drift: `codegraph drift ./src --base origin/main --head HEAD --pretty --graph-edges summary --public-api removals`
 - installer: `codegraph install --target codex,claude --dry-run`
@@ -64,6 +65,7 @@ Current high-value surfaces:
 - `orient --pretty`: ranked first-turn focus targets with copyable follow-ups
 - `impact --pretty`: ranked "what could this break?" map
 - `review --summary`: compact reviewer handoff
+- `affected --quiet`: deterministic path-only test selection for a changed-file set
 - `duplicates --profile cleanup`: refactor ROI ordering
 - `duplicates --json`: full grouped duplicate data
 
@@ -78,7 +80,8 @@ Fall back to CLI when MCP is unavailable.
 
 ## Discovery
 
-Durable repo-local ignores belong in `codegraph.config.json`.
+Durable repo-local ignores and custom language suffixes belong in `codegraph.config.json`.
+Use `languages.extensions` for literal suffix-to-language mappings such as `.tpl` to `php`; keys start with `.`, may contain letters, digits, `.`, `_`, `+`, and `-`, and values are supported language IDs. The longest suffix wins; `.vue` and `.svelte` are always handled as single-file components and cannot be remapped.
 One-off CLI filters use scan-root-relative `--include-glob` and `--ignore-glob`.
 Use `--no-gitignore` only when ignored files are intentionally in scope.
 

docs/cli.md

@@ -14,6 +14,7 @@ Default workflow:
 
 - code review: `codegraph review --base HEAD --head WORKTREE --summary`
 - blast-radius follow-up: `codegraph impact --base HEAD --head WORKTREE --pretty`
+- affected tests: `codegraph affected --base HEAD --head WORKTREE --quiet`
 - unfamiliar repo: `codegraph explore "how does auth reach db?" --root . --pretty`
 - first-turn map: `codegraph orient --root . --budget small --pretty`
 - targeted follow-up: `codegraph search "<query>" --json` then `codegraph explain <handle|file|symbol>`
@@ -35,18 +36,27 @@ Commands that scan a project read `codegraph.config.json` from `--root` when it
     "includeGlobs": ["src/**/*.ts"],
     "ignoreGlobs": ["tests/samples/**", "tests/languages/samples/**"],
     "useGitignore": true
+  },
+  "languages": {
+    "extensions": {
+      ".tpl": "php",
+      ".inc.php": "php",
+      ".build.ts": "ts"
+    }
   }
 }
 ```
 
 - `discovery.includeGlobs` and `discovery.ignoreGlobs` are project-root-relative, even when a command scans child include roots.
 - `discovery.ignoreGlobs` is for large fixture, generated, or vendored folders that should not be indexed.
+- `languages.extensions` maps additional or built-in literal suffixes to supported language IDs; keys must start with `.` and may contain letters, digits, `.`, `_`, `+`, and `-`, values must name a supported language, and the longest suffix wins.
+- Built-in suffixes remain active unless explicitly remapped by `languages.extensions`; `.vue` and `.svelte` are always handled as single-file components and cannot be remapped.
 - CLI `--include-glob` and `--ignore-glob` values are one-off additions relative to each scanned root.
 - `inspect` follow-up commands preserve the selected `--root` and include roots.
 - `--no-gitignore` overrides `useGitignore`.
 
 Config globs and one-off CLI globs apply at different layers. `codegraph.config.json` globs are durable and project-root-relative. CLI scan-root globs are additive for a single command and are evaluated relative to each active scan root. `--no-gitignore` disables `.gitignore` filtering for that command only; it does not change config.
-Cache and manifest reuse is rooted at `--root`. Reusing a project root lets commands share compatible index and graph entries when the file signatures, config, graph options, and relevant build options still match. Changing `--root`, changing discovery config, or changing graph options creates a different reuse boundary. Child include-root scans can reuse project-root cache entries, but command summaries and follow-up commands stay scoped to the selected include roots.
+Configured language extensions automatically extend discovery for matching files and participate in cache compatibility checks. Reusing a project root lets commands share compatible index and graph entries when the file signatures, config, graph options, and relevant build options still match. Changing `--root`, changing discovery or language-extension config, or changing graph options creates a different reuse boundary. Child include-root scans can reuse project-root cache entries, but command summaries and follow-up commands stay scoped to the selected include roots.
 
 ## Core commands
 
@@ -56,6 +66,7 @@ Cache and manifest reuse is rooted at `--root`. Reusing a project root lets comm
 # Fast code-review handoff for current local edits
 codegraph review --base HEAD --head WORKTREE --summary
 codegraph impact --base HEAD --head WORKTREE --pretty
+codegraph affected --base HEAD --head WORKTREE --quiet
 
 # First-pass repo summary and next-step suggestions
 codegraph orient --root . --budget small --pretty
@@ -125,6 +136,19 @@ Graph, index, and review reports include `backend.native.byLanguage` so native u
 - `uninit` removes only recognized lifecycle state by default. It refuses unknown `.codegraph/` entries unless `--force` is passed.
 - Lifecycle commands accept either a positional project path or `--root <path>`. They reject using both together because lifecycle manifests always describe one project boundary, not include-root subsets.
 
+### Affected tests
+
+- `affected` maps changed source files to likely test files by traversing reverse dependencies through the project graph. It also includes directly changed test files at depth 0.
+- Inputs can be positional files, newline-delimited `--stdin`, or a Git range with `--base <ref> --head <ref>`. Paths are normalized under `--root` and output as project-root-relative paths.
+- Use `--depth <n>` to expand transitive reverse dependencies, `--filter <glob>` to restrict returned test paths, `--quiet` for path-only output, or `--json` for `schemaVersion: 1`, `changedFiles`, `affectedTests`, and `omittedCounts`.
+
+```bash
+codegraph affected src/auth.ts src/db.ts
+codegraph affected --stdin --quiet
+codegraph affected --base main --head HEAD --json
+codegraph affected --base HEAD --head WORKTREE --filter "tests/**/*.test.ts" --quiet
+```
+
 ### Symbols, navigation, grep, and chunking
 
 ```bash

docs/library-api.md

@@ -28,7 +28,7 @@ For repeated calls, prefer one warm session instead of rebuilding indexes ad hoc
 - `createCodeReviewSession()` for repeated navigation and impact work in library code
 - `createAgentSession()` or MCP for repeated orient/search/explain/packet work in agent hosts
 
-CLI commands and agent sessions read `codegraph.config.json` from the project root when it exists. Core indexing APIs keep discovery explicit, so pass `discovery` options directly when you want the same scan scope in custom code:
+CLI commands and agent sessions read `codegraph.config.json` from the project root when it exists. Core indexing APIs keep discovery and language mappings explicit, so pass both options directly when you want the same behavior in custom code:
 
 ```ts
 import { buildProjectIndex, loadCodegraphConfig } from "@lzehrung/codegraph";
@@ -37,9 +37,12 @@ const root = process.cwd();
 const config = await loadCodegraphConfig(root);
 const index = await buildProjectIndex(root, {
   ...(config.discovery ? { discovery: config.discovery } : {}),
+  ...(config.languages?.extensions ? { languageExtensions: config.languages.extensions } : {}),
 });
 ```
 
+`languageExtensions` uses normalized literal suffixes beginning with `.`, supported language IDs, and longest-suffix matching. Suffixes may contain letters, digits, `.`, `_`, `+`, and `-`; `.vue` and `.svelte` remain single-file components and cannot be remapped.
+
 ## Public API Boundary
 
 The npm package exposes these supported entry points:

docs/plans/2026-07-03-16-config-extension-mapping.md

@@ -35,10 +35,10 @@ type CodegraphConfig = {
 
 Rules:
 
-- Extension keys must start with `.`.
+- Extension keys must be literal suffixes starting with `.` and containing only letters, digits, `.`, `_`, `+`, or `-`.
 - Values must be supported language ids.
 - Longer extension keys win first, so `.inc.php` beats `.php`.
-- Built-in extensions remain unless explicitly remapped.
+- Built-in extensions remain unless explicitly remapped; `.vue` and `.svelte` remain single-file components and cannot be remapped.
 - Invalid mappings fail config validation with actionable errors.
 
 ## Integration

src/agent/session.ts

@@ -5,8 +5,9 @@ import type { BuildOptions, BuildReport, ProjectIndex } from "../indexer/types.j
 import { buildSymbolGraphDetailed } from "../graphs/symbol-graph-detailed.js";
 import { type SymbolGraph } from "../graphs/symbol-graph.js";
 import type { Graph } from "../types.js";
-import { listProjectFiles, type ProjectFileDiscoveryOptions } from "../util/projectFiles.js";
+import { DEFAULT_PROJECT_PATTERNS, listProjectFiles, type ProjectFileDiscoveryOptions } from "../util/projectFiles.js";
 import { hasDiscoveryOptions, loadCodegraphConfig, mergeDiscoveryOptions } from "../config.js";
+import { languageExtensionPatterns, normalizeLanguageExtensions } from "../languages.js";
 import { createAgentFileLookup } from "./normalize.js";
 import { summarizeAnalysis, type AnalysisSummary } from "../analysisSummary.js";
 
@@ -81,6 +82,7 @@ export type AgentFileSignature = {
 
 type AgentDiscoverySettings = {
   discoveryOptions?: ProjectFileDiscoveryOptions;
+  languageExtensions?: BuildOptions["languageExtensions"];
 };
 
 type AgentFreshnessDiff = {
@@ -96,12 +98,19 @@ async function resolveAgentDiscoverySettings(options: AgentSessionOptions): Prom
   const discoveryOptions = hasDiscoveryOptions(discovery)
     ? { ...discovery, globRoot: discovery.globRoot ?? options.root }
     : undefined;
-  return discoveryOptions ? { discoveryOptions } : {};
+  const languageExtensions =
+    normalizeLanguageExtensions(options.buildOptions?.languageExtensions) ?? config.languages?.extensions;
+  return {
+    ...(discoveryOptions ? { discoveryOptions } : {}),
+    ...(languageExtensions ? { languageExtensions } : {}),
+  };
 }
 
 export async function listAgentSessionFiles(options: AgentSessionOptions): Promise<string[]> {
-  const { discoveryOptions } = await resolveAgentDiscoverySettings(options);
-  return await listProjectFiles(options.root, undefined, discoveryOptions);
+  const { discoveryOptions, languageExtensions } = await resolveAgentDiscoverySettings(options);
+  const customPatterns = languageExtensionPatterns(languageExtensions);
+  const patterns = customPatterns.length ? [...DEFAULT_PROJECT_PATTERNS, ...customPatterns] : undefined;
+  return await listProjectFiles(options.root, patterns, discoveryOptions);
 }
 
 function isMissingStatRace(error: unknown): boolean {
@@ -200,7 +209,7 @@ export function createAgentSession(options: AgentSessionOptions): AgentSession {
   const loadBase = async (): Promise<AgentProjectBaseSnapshot> => {
     if (cachedBase) return cachedBase;
     const loadPromise = (async () => {
-      const { discoveryOptions } = await resolveAgentDiscoverySettings(options);
+      const { discoveryOptions, languageExtensions } = await resolveAgentDiscoverySettings(options);
       const files = await loadFiles();
       cachedFileSignatures = await collectAgentFileSignatures(files);
       const buildOptions: BuildOptions & { files: string[] } = {
@@ -209,6 +218,7 @@ export function createAgentSession(options: AgentSessionOptions): AgentSession {
         keepParsed: options.buildOptions?.keepParsed ?? true,
         files,
         ...(discoveryOptions ? { discovery: discoveryOptions } : {}),
+        ...(languageExtensions ? { languageExtensions } : {}),
       };
       if (
         options.buildOptions?.useNativeWorkers === undefined &&