[Bug] MCP tool calls double-dispatched with different tool_use_ids

Bug Description
Claude Code Double-Dispatches Every MCP Tool Call

Environment: Claude Code 2.1.79, Windows 11, MCP server via cmd /c npx -y @k-system/tickr-mcp (stdio transport)

Problem: Every single MCP tool call is executed exactly twice with identical parameters, ~2-4ms apart. This affects ALL tools (read, write, create, update,
delete) — not just specific ones.

Evidence from MCP debug log:
[09:57:25.661Z] [create_ticket] params={...} → ok (555ms)
[09:57:25.794Z] [create_ticket] params={...} → ok (689ms) ← DUPLICATE

[09:57:33.409Z] [update_ticket] params={...} → error (406ms)
[09:57:34.010Z] [update_ticket] params={...} → ok (1008ms) ← DUPLICATE (causes concurrency error)

[09:41:25.195Z] [create_implementation_item] params={...} → ok (226ms)
[09:41:25.203Z] [create_implementation_item] params={...} → ok (234ms) ← DUPLICATE

Impact:

• CREATE operations produce duplicate records (two tickets, two comments, two relations)
• UPDATE operations cause DbUpdateConcurrencyException — first call succeeds, second fails because entity was already modified
• DELETE operations cause DbUpdateConcurrencyException — first deletes, second finds nothing

What we ruled out:

• Not a retry (retries have 100ms+ delay, these are 2-4ms apart)
• Not duplicate MCP server registration (verified single registration in .claude.json)
• Not agent/team configuration (happens with and without agent features)
• Not MCP server bug (server receives two separate calls — confirmed by debug logging)
• Colleague with identical setup on different machine does NOT have duplicates

Related GitHub issues:

• https://github.com/anthropics/claude-code/issues/22658 — "MCP tool calls duplicated multiple times when using parallel subagents" (closed as duplicate)
• https://github.com/anthropics/claude-code/issues/13897 — "Agent calls tools twice after permission approval" (closed as NOT PLANNED)
• https://github.com/anthropics/claude-code/issues/14253 — "Messages sent during Task agent execution are delivered twice"

Workaround attempted: MCP server-side dedup using tool_use_id cache. However, both duplicate calls appear to have different tool_use_ids, so the dedup only
catches Claude Code's subsequent retries, not the initial double-dispatch.

Current mitigation: API-side DedupHash with UNIQUE constraint on create endpoints + graceful catch of DbUpdateException. This prevents duplicate records but
doesn't stop the unnecessary second API call.

Environment Info

• Platform: win32
• Terminal: WezTerm
• Version: 2.1.79
• Feedback ID: f4a1a330-4233-4856-bd0d-c1bee7e5828d

Errors

[{"error":"Error: Tool mcp__tickr__list_tickets not found\n    at CY8 (B:/~BUN/root/src/entrypoints/cli.js:2802:48341)\n    at _K (B:/~BUN/root/src/entrypoints/cli.js:698:20995)\n    at MK (B:/~BUN/root/src/entrypoints/cli.js:698:39537)\n    at oO (B:/~BUN/root/src/entrypoints/cli.js:698:50228)\n    at zkH (B:/~BUN/root/src/entrypoints/cli.js:698:86972)\n    at OkH (B:/~BUN/root/src/entrypoints/cli.js:698:85934)\n    at PkH (B:/~BUN/root/src/entrypoints/cli.js:698:85756)\n    at qsH (B:/~BUN/root/src/entrypoints/cli.js:698:82114)\n    at vH (B:/~BUN/root/src/entrypoints/cli.js:698:6492)\n    at VH (B:/~BUN/root/src/entrypoints/cli.js:698:4974)","timestamp":"2026-03-19T09:03:04.140Z"},{"error":"Error: Tool mcp__tickr__list_tickets not found\n    at CY8 (B:/~BUN/root/src/entrypoints/cli.js:2802:48341)\n    at _K (B:/~BUN/root/src/entrypoints/cli.js:698:20995)\n    at MK (B:/~BUN/root/src/entrypoints/cli.js:698:39537)\n    at oO (B:/~BUN/root/src/entrypoints/cli.js:698:50228)\n    at zkH (B:/~BUN/root/src/entrypoints/cli.js:698:86972)\n    at OkH (B:/~BUN/root/src/entrypoints/cli.js:698:85934)\n    at PkH (B:/~BUN/root/src/entrypoints/cli.js:698:85756)\n    at qsH (B:/~BUN/root/src/entrypoints/cli.js:698:82114)\n    at vH (B:/~BUN/root/src/entrypoints/cli.js:698:6492)\n    at VH (B:/~BUN/root/src/entrypoints/cli.js:698:4974)","timestamp":"2026-03-19T09:03:04.140Z"},{"error":"Error: Tool mcp__tickr__list_tickets not found\n    at CY8 (B:/~BUN/root/src/entrypoints/cli.js:2802:48341)\n    at _K (B:/~BUN/root/src/entrypoints/cli.js:698:20995)\n    at MK (B:/~BUN/root/src/entrypoints/cli.js:698:39537)\n    at oO (B:/~BUN/root/src/entrypoints/cli.js:698:50228)\n    at zkH (B:/~BUN/root/src/entrypoints/cli.js:698:86972)\n    at OkH (B:/~BUN/root/src/entrypoints/cli.js:698:85934)\n    at PkH (B:/~BUN/root/src/entrypoints/cli.js:698:85756)\n    at qsH (B:/~BUN/root/src/entrypoints/cli.js:698:82114)\n    at vH (B:/~BUN/root/src/entrypoints/cli.js:698:6492)\n    at VH (B:/~BUN/root/src/entrypoints/cli.js:698:4974)","timestamp":"2026-03-19T09:03:04.140Z"},{"error":"Error: To…

Note: Content was truncated.