Server-tool call counter in /usage

What it does

Counts, per session, the calls a provider ran for a configured server tool, and shows the count as a row in /usage.

Source

ganja-code-g20i (a per-session server-tool call counter in /usage).

The bead is closed when this issue is published, with its external reference pointing here (#38).

File and line references in this issue are to main as of 75a7a92.

Against the three criteria

• Direction (README): The README's only word on cost is that 10,000 subagents "is a budget question" (README.md:28-29).
• Today's terminal users: A configured server tool bills per call and nothing counts the calls; the billing is why D489 made server tools opt-in.
• Evidence: D563's plan named the counter as a risk mitigation and deferred it. The event already carries the tool's name (ProviderEvent::ServerTool).

Depends on

Nothing. The work is a fold in the engine plus one row in /usage.

Verdict

• Verdict: do
• Size: S — one commit, no plan.
• Exception to the probe rule: no.
• Date: 2026-09-19
• Verdict ticket: #45

Theme: #58

Start with the engine handling ProviderEvent::ServerTool and trace how the per-session state is folded into the /usage view. Confirm the configured server tool name is available in the event, then add the usage row and verify that its count is correct for each session.