fix(cli): register the documented context command (#1611) (#1613)

Fixes #1611.

## What

`codegraph context <task>` has been advertised in the CLI usage header since the first commit, and the ContextBuilder behind the public `buildContext` API has always shipped in the package — but the command was never registered with commander (verified via `git log -S`: this is drift present from day one, not a removal). Invoking it errored with `unknown command 'context'`, which broke external integrations built against the documented contract — Memorix 1.8.1 invokes `codegraph context --path <project-root> --format json --max-nodes 8 --no-code <task>` and silently falls back to its own heuristic index when the command is missing.

## How

Registers `context <task...>` next to the other read commands (`query`/`explore` pattern), mapping flags 1:1 onto `BuildContextOptions`:

- `-p, --path <path>` — resolved exactly like every sibling command (nearest initialized project)
- `-f, --format <format>` — `markdown` (default) or `json`, unknown values rejected with exit 1
- `-n, --max-nodes <number>` — positive integer, validated
- `--no-code` — structure only (`includeCode: false`)

JSON output is clean, machine-parseable stdout — `error()` and warnings go to stderr — and the uninitialized-project path matches the sibling commands' error text and exit code. The usage-header line needed no change; the registered syntax matches what it has always advertised.

## Tested

New `__tests__/cli-context-command.test.ts` (modeled on `cli-query-command.test.ts`, spawning the built binary against a temp fixture): JSON parseability + shape, `--max-nodes` bounding, the exact Memorix invocation shape (`--format json --max-nodes 8 --no-code`), markdown default, uninitialized-project failure, unknown-format rejection. `npx vitest run __tests__/cli-context-command.test.ts __tests__/context.test.ts __tests__/context-ranking.test.ts __tests__/cli-query-command.test.ts` → 4 files, 39 tests, all green.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01LxZj6W6Y1SHXwvpT3uwJpK

src/bin/codegraph.ts

@@ -1250,6 +1250,65 @@ program
     }
   });
 
+/**
+ * codegraph context <task...>
+ *
+ * The CLI face of the public `buildContext` API (ContextBuilder): FTS entry
+ * points + graph expansion + code blocks, formatted as markdown or JSON.
+ * Advertised in the usage header since the first release but never actually
+ * registered (#1611); external integrations (e.g. Memorix) invoke it as
+ * `codegraph context --path <root> --format json --max-nodes 8 --no-code <task>`.
+ */
+program
+  .command('context <task...>')
+  .description('Build context for a task: relevant symbols, relationships, and code blocks')
+  .option('-p, --path <path>', 'Project path')
+  .option('-f, --format <format>', 'Output format: markdown or json', 'markdown')
+  .option('-n, --max-nodes <number>', 'Maximum number of symbols to include')
+  .option('--no-code', 'Omit code blocks (structure only)')
+  .action(async (taskParts: string[], options: { path?: string; format?: string; maxNodes?: string; code?: boolean }) => {
+    const projectPath = resolveProjectPath(options.path);
+
+    const format = options.format ?? 'markdown';
+    if (format !== 'markdown' && format !== 'json') {
+      error(`Unknown format "${options.format}" — use "markdown" or "json".`);
+      process.exit(1);
+    }
+    let maxNodes: number | undefined;
+    if (options.maxNodes !== undefined) {
+      maxNodes = parseInt(options.maxNodes, 10);
+      if (Number.isNaN(maxNodes) || maxNodes < 1) {
+        error(`--max-nodes expects a positive integer, got "${options.maxNodes}".`);
+        process.exit(1);
+      }
+    }
+
+    try {
+      if (!isInitialized(projectPath)) {
+        error(`CodeGraph not initialized in ${projectPath}`);
+        process.exit(1);
+      }
+
+      const { default: CodeGraph } = await loadCodeGraph();
+      const cg = await CodeGraph.open(projectPath);
+
+      const result = await cg.buildContext(taskParts.join(' '), {
+        format,
+        includeCode: options.code !== false,
+        ...(maxNodes !== undefined ? { maxNodes } : {}),
+      });
+
+      // Both supported formats return a formatted string; print it verbatim so
+      // `--format json` stays machine-parseable on stdout (error()/warnings go
+      // to stderr only).
+      console.log(typeof result === 'string' ? result : JSON.stringify(result, null, 2));
+      cg.destroy();
+    } catch (err) {
+      error(`Context build failed: ${err instanceof Error ? err.message : String(err)}`);
+      process.exit(1);
+    }
+  });
+
 /**
  * codegraph prompt-hook  (hidden)
  *