fix(telemetry): namespace tool_call span under :anubis_mcp

[acollado-g2]

Summary

Fixes #243. Anubis.Server.Session's tool_call telemetry span was firing under [:server, :tool_call, :start | :stop | :exception] — without the :anubis_mcp namespace prefix every other server-side telemetry event in the library gets.

Root cause

Every telemetry call site in lib/anubis/server/session.ex goes through Anubis.Telemetry.execute/3, which prepends the prefix:

def execute(event_name, measurements, metadata) do
  :telemetry.execute([:anubis_mcp | event_name], measurements, metadata)
end

Anubis.Telemetry.event_server_tool_call/0 — like every sibling event_* function — is documented as returning "the event name, excluding the :anubis_mcp prefix", i.e. meant to be passed through execute/3. The one :telemetry.span/3 call wrapping tools/call, however, passed this value straight to :telemetry.span/3, bypassing execute/3 entirely — so the real events fired were unprefixed.

Fix

One-line change: prepend :anubis_mcp to the span's event prefix, matching every other event in the file.

:telemetry.span(
  [:anubis_mcp | Telemetry.event_server_tool_call()],
  %{tool: tool_name},
  fn -> {module.handle_request(request, frame), %{tool: tool_name}} end
)

Testing

• Added a regression test in test/anubis/server/session_async_dispatch_test.exs (describe "tool_call telemetry") attaching to [:anubis_mcp, :server, :tool_call, :stop] and asserting it fires on a real tools/call dispatch through a live Session.
• Verified the new test fails without the fix (reverted the one-line change locally, test failed with "no matching message after 1000ms" — the unprefixed event doesn't match) and passes with it.
• Full suite: mix test → 941 tests, 35 doctests, 0 failures.
• mix lint (format --check-formatted, credo --strict, dialyzer) → clean.

Impact

Any application instrumenting Anubis's native telemetry via the documented [:anubis_mcp | ...] convention would silently receive zero tool-call metrics/spans while correctly receiving every other server event (request, response, error, init, etc) — no error, no warning, just a metric that never fires. Discovered while wiring Datadog metrics for tool-call latency in a downstream application.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 9cc4b249-7017-42c7-8062-3d5e5772562c

📥 Commits

Reviewing files that changed from the base of the PR and between 2451bb7 and c9a3219.

📒 Files selected for processing (2)

• lib/anubis/server/session.ex
• test/anubis/server/session_async_dispatch_test.exs

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📝 Walkthrough

Problem

Tool-call telemetry events lacked the :anubis_mcp namespace.

Solution

Prefix tool_call span events with :anubis_mcp.

Rationale

Aligns telemetry with the documented convention and adds regression coverage for the namespaced :stop event.

Walkthrough

Anubis.Server.Session now prefixes tools/call telemetry spans with :anubis_mcp. A test attaches a handler for the namespaced stop event, executes an "echo" tool call, and verifies the duration and tool metadata before detaching the handler.

Possibly related PRs

• zoedsoupe/anubis-mcp#153: Related session tools/call telemetry instrumentation and testing.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description is complete, but it does not use the required Problem/Solution/Rationale template headings.	Rewrite the PR description using the repository template sections: Problem, Solution, and Rationale, with the key details under each.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise and accurately summarizes the telemetry namespace fix.
Linked Issues check	✅ Passed	The change and regression test directly address issue #243 by namespacing the tool_call telemetry span.
Out of Scope Changes check	✅ Passed	The only code and test changes are tightly scoped to the telemetry namespace fix and its regression coverage.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

✨ Simplify code

• Create PR with simplified code

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