[BUG] Plugin-registered hooks are executed twice with different PIDs

Found 3 possible duplicate issues:

1. https://github.com/anthropics/claude-code/issues/3465
2. https://github.com/anthropics/claude-code/issues/3523
3. https://github.com/anthropics/claude-code/issues/9602

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🤖 Generated with Claude Code

This issue is not a duplicate of the suggested issues:

• #3465: Only occurred when running from home directory. This issue occurs regardless of working directory and is specific to plugin-registered hooks.

• #3523: Hooks progressively duplicated (2x→5x→10x+) during sessions. This issue shows consistent 2x execution from the start, not progressive.

• #9602: UI rendering bug only - hooks executed once but UI showed duplicates. This issue involves actual duplicate execution with different PIDs (proven via log files showing two separate processes).

Key distinction: This is a plugin hook registration issue causing real duplicate execution, verified by different process IDs in logs.

🤖 by Claude Code

I've resolved this issue myself. Apologies for the confusion!

Root Cause

The duplicate hook execution was caused by the same file being loaded twice in the plugin system's hook loading process.

How It Happens

1. Automatic loading of default path

• hooks/hooks.json is automatically loaded if it exists

1. Loading from plugin.json's hooks field

• When plugin.json contains "hooks": "./hooks/hooks.json", the same file is loaded again

1. Hook merge process

• The merge function (yGQ) simply concatenates arrays without checking for duplicates
• This results in the same hooks being registered twice

Problem in the Test Plugin

The issue was in my test plugin's plugin.json:

{
  "name": "hook-duplicate-test",
  "hooks": "./hooks/hooks.json"  // ← This causes the duplication
}

Removing this field (or specifying a different path than the default) prevents the duplication.

Code Investigation

I couldn't find the unminified source code, but Claude Code (Sonnet 4.5) analyzed the minified cli.js and identified the problem areas.

Plugin loading process (relevant part of _GQ function):

// 1. Automatic loading of default path
let V, K = XI(A, "hooks", "hooks.json");  // path to hooks/hooks.json
if (G.existsSync(K))
  try {
    V = SGQ(K, J.name)  // ← First load
  } catch (D) { ... }

// 2. Processing plugin.json's hooks field
if (J.hooks) {  // J.hooks is the hooks field from plugin.json
  let D = Array.isArray(J.hooks) ? J.hooks : [J.hooks];
  for (let E of D)
    if (typeof E === "string") {  // E = "./hooks/hooks.json"
      let H = XI(A, E);
      if (!G.existsSync(H)) { ... continue }
      try {
        let w = SGQ(H, J.name);  // ← Second load (same file!)
        V = yGQ(V, w)  // ← Merge causes duplication
      } catch (w) { ... }
    }
}

Hook merge process (yGQ function):

function yGQ(A, B) {
  if (!A) return B;
  let Q = {...A};
  for (let [I, G] of Object.entries(B))
    if (!Q[I])
      Q[I] = G;
    else 
      Q[I] = [...Q[I] || [], ...G];  // ← Concatenates arrays (no duplicate check)
  return Q
}

Suggestion

Since this issue is subtle and easy to miss, I think it would be helpful to prevent duplicate file loading by comparing absolute paths. Tracking already-loaded file paths would prevent the same file from being loaded twice.

This issue can now be closed.

Thanks for your report!

In https://github.com/otolab/hook-duplicate-test-plugin/blob/main/plugins/hook-duplicate-test/.claude-plugin/plugin.json , you shouldn't specify "hooks": "./hooks/hooks.json" because we already load the hooks folder automatically. This "hooks" field in the JSON causes the duplicate registration -- it's meant for registering extra hooks not already automatically imported.

However, this is quite the footgun, so I'm leaving this open for the team to figure out the best handle this situation.

Thanks for confirming this is a known issue. I'll look forward to the team's decision on the best approach to handle this.

This issue has been inactive for 30 days. If the issue is still occurring, please comment to let us know. Otherwise, this issue will be automatically closed in 30 days for housekeeping purposes.

Still hitting this on 2.0.x (latest). Seeing 4x output for bumper-lanes plugin hooks:

PostToolUse:Bash hook returned blocking error: ✓ Bumper lanes: Auto-reset after commit.
PostToolUse:Callback hook returned blocking error: ✓ Bumper lanes: Auto-reset after commit.
PostToolUse:Bash hook returned blocking error: ✓ Bumper lanes: Auto-reset after commit.
PostToolUse:Callback hook returned blocking error: ✓ Bumper lanes: Auto-reset after commit.

The 4x is: 2 tool matchers × 2 duplicate executions (the bug).

This is particularly noisy for hooks that provide user feedback since every message gets doubled. Would love to see this prioritized - it's been open since early November.

See also #14281 which reports the same symptom from the hook additionalContext angle.

@dicksontai The bumper-lanes plugin (source) does not have a "hooks" field in plugin.json - it only uses auto-discovery from the hooks/ folder:

{
  "name": "claude-bumper-lanes",
  "version": "3.0.0",
  "description": "Enforces git diff thresholds...",
  ...
}

Yet we still see duplicate execution:

PostToolUse:Bash hook returned blocking error: ✓ Bumper lanes: Auto-reset
PostToolUse:Callback hook returned blocking error: ✓ Bumper lanes: Auto-reset
PostToolUse:Bash hook returned blocking error: ✓ Bumper lanes: Auto-reset
PostToolUse:Callback hook returned blocking error: ✓ Bumper lanes: Auto-reset

So the duplicate execution bug exists independently of the "hooks" footgun.

<img width="652" height="244" alt="Image" src="https://github.com/user-attachments/assets/86147313-5321-4bf6-87b8-59a6581ab26a" />

<img width="655" height="113" alt="Image" src="https://github.com/user-attachments/assets/14115bad-f619-4a25-8074-38f98d3f80a1" />

@dhollman / @dicksontsai
Can you review my plugin configurations and double check it's not user error?
https://github.com/kylesnowschwartz/SimpleClaude/tree/main/plugins/sc-hooks
https://github.com/kylesnowschwartz/claude-bumper-lanes/tree/main/bumper-lanes-plugin

Is it possible that plugin hooks from the plugins/cache dir and plugins/marketplaces dir are causing duplicate hook registrations? Notice even the Anthropic 'ralph-wiggum' hook is listed twice.

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