How GitNexus Detects Staleness and Triggers Re-Indexing

GitNexus detects staleness by executing git rev-list --count to compare the indexed last commit hash against the current HEAD, returning a staleness hint when new commits are detected.

GitNexus maintains an internal graph index that must stay synchronized with the underlying Git repository to provide accurate code intelligence. To ensure the index reflects the latest state without unnecessary rebuilds, GitNexus implements a lightweight staleness detection mechanism that checks whether the stored commit is behind HEAD before every context request.

The Core Staleness Detection Algorithm

The checkStaleness Function

The staleness logic lives in gitnexus/src/mcp/staleness.ts inside the checkStaleness function. This utility accepts a repository path and the last indexed commit hash, then returns a StalenessInfo object indicating whether the index is outdated.

// https://github.com/abhigyanpatwari/GitNexus/blob/main/gitnexus/src/mcp/staleness.ts
export function checkStaleness(repoPath: string, lastCommit: string): StalenessInfo {
  try {
    // Count how many commits are between the stored lastCommit and the current HEAD
    const result = execFileSync(
      'git', ['rev-list', '--count', `${lastCommit}..HEAD`],
      { cwd: repoPath, encoding: 'utf-8', stdio: ['pipe', 'pipe', 'pipe'] }
    ).trim();

    const commitsBehind = parseInt(result, 10) || 0;

    if (commitsBehind > 0) {
      // Index is stale – return a hint for the LLM / user
      return {
        isStale: true,
        commitsBehind,
        hint: `⚠️ Index is ${commitsBehind} commit${commitsBehind > 1 ? 's' : ''} behind HEAD. Run analyze tool to update.`,
      };
    }

    // Index is up‑to‑date
    return { isStale: false, commitsBehind: 0 };
  } catch {
    // If the git command fails (e.g., not a git repo), assume “not stale” – fail‑open
    return { isStale: false, commitsBehind: 0 };
  }
}

How the Git Command Works

The detection relies on git rev-list --count <lastCommit>..HEAD, which returns the number of commits reachable from HEAD but not from the stored lastCommit. This count, stored as commitsBehind, serves as the single source of truth for staleness:

• Zero commits behind: The index is current.
• One or more commits behind: The index is stale and requires rebuilding.

Where Staleness Checks Are Triggered

GitNexus evaluates staleness at multiple integration points to ensure users and LLM agents always receive accurate metadata.

Context Resource Requests

In gitnexus/src/mcp/resources.ts, every request for the repository context resource (gitnexus://repo/{name}/context) invokes checkStaleness. If stale, the handler appends the hint directly to the resource output:

// https://github.com/abhigyanpatwari/GitNexus/blob/main/gitnexus/src/mcp/resources.ts
const staleness = repoPath ? checkStaleness(repoPath, lastCommit) : { isStale: false, commitsBehind: 0 };
if (staleness.isStale && staleness.hint) {
  lines.push('');
  lines.push(`staleness: "${staleness.hint}"`);
}

CLI Status Command

The gitnexus status command, implemented in gitnexus/src/cli/status.ts, surfaces staleness to terminal users:

// https://github.com/abhigyanpatwari/GitNexus/blob/main/gitnexus/src/cli/status.ts
console.log(`Status: ${isUpToDate ? '✅ up-to-date' : '⚠️ stale (re-run gitnexus analyze)'}`);

Post-Tool-Use Hooks

After mutation tools (such as gitnexus rename) execute, the framework re-evaluates staleness via post-tool-use hooks. This ensures that any changes made to the repository are immediately reflected in subsequent staleness checks, preventing the LLM from acting on outdated graph data.

Handling Stale Index States

The Staleness Hint System

When checkStaleness detects divergence, it generates a hint string that includes:

• The exact number of commits behind.
• A specific remediation command (Run analyze tool to update).

This hint is injected into MCP resource responses, allowing LLM agents to parse the warning and automatically suggest the analyze tool invocation to the user.

Fail-Open Safety Mechanism

If the git rev-list command throws (for example, if the path is not a Git repository or Git is not installed), checkStaleness catches the exception and returns isStale: false. This fail-open design prevents the system from blocking operations due to environmental issues while logging the error for debugging.

Re-indexing Workflow

When staleness is detected, users or agents must trigger a re-index using the analyze command:

# Rebuild the graph index from the current HEAD

npx gitnexus analyze

Programmatically, you can check staleness before deciding to re-index:

import { checkStaleness } from 'gitnexus/src/mcp/staleness.js';

const repoPath = '/path/to/repo';
const lastIndexedCommit = 'a1b2c3d';   // stored in meta.json
const { isStale, commitsBehind, hint } = checkStaleness(repoPath, lastIndexedCommit);

if (isStale) {
  console.warn(hint);   // => "⚠️ Index is 2 commits behind HEAD. Run analyze tool to update."
  // Trigger re-indexing logic here
}

Summary

• Staleness detection relies on git rev-list --count to compare the indexed commit hash with the current HEAD, calculating exactly how many commits the index lags behind.
• The checkStaleness function in gitnexus/src/mcp/staleness.ts executes this check and returns a structured StalenessInfo object containing a human-readable hint when the index is outdated.
• Staleness is evaluated on every context resource request, during CLI status checks, and after mutation tool execution to ensure the graph index remains synchronized with the repository.
• The system implements a fail-open policy, returning isStale: false if Git commands fail, preventing operational blockages while maintaining safety.
• When staleness is detected, users and LLM agents are instructed to run npx gitnexus analyze to rebuild the index from the current HEAD.

Frequently Asked Questions

How does GitNexus detect staleness without scanning the entire repository?

GitNexus detects staleness by executing a lightweight Git command rather than re-scanning files. The checkStaleness function runs git rev-list --count <lastCommit>..HEAD, which returns only the number of commits between the stored index commit and the current HEAD. This operation is O(1) relative to repository size and avoids the expensive I/O of re-parsing the entire codebase.

What happens if the git rev-list command fails during staleness detection?

If the git rev-list command throws an exception—such as when the path is not a Git repository or Git is not installed—the checkStaleness function catches the error and returns isStale: false with commitsBehind: 0. This fail-open behavior ensures that transient environment issues do not block the MCP server or CLI operations, though the error is silently handled to prevent crashes.

How often does GitNexus check for staleness?

GitNexus checks for staleness on every request for the repository context resource (gitnexus://repo/{name}/context), ensuring that LLM agents receive immediate feedback about index currency. Additionally, the check runs when users execute the gitnexus status CLI command and after any mutation tool (like rename) completes, providing multiple synchronization points without requiring a background daemon.

Can I force a re-index even if GitNexus doesn't detect staleness?

Yes, you can force a re-index at any time by running npx gitnexus analyze, regardless of the staleness state. This command rebuilds the graph index from the current HEAD and updates the stored lastCommit hash. Forcing a re-index is useful when you suspect the index metadata is corrupted or when you want to ensure the graph reflects the exact state of the repository after external changes that might not trigger the standard staleness detection.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}