fix(mcp): default get-llm-total-costs-for-project to active project

[Radu-Raicea]

Problem

The get-llm-total-costs-for-project MCP tool declares projectId as a required input. Agents don't know the numeric project id, so a large share of this tool's calls fail validation with missing required parameter: projectId (visible in the MCP tool-call analytics). Every other tool in the server resolves the project from context via context.stateManager.getProjectId().

Changes

• Make projectId optional on AIObservabilityGetCostsSchema, with a description noting it defaults to the active project.
• In the handler, fall back to context.stateManager.getProjectId() when projectId is omitted, dropping the now-redundant String() wrap. This aligns the tool with the getProjectId() convention documented in src/tools/README.md.
• Regenerated the shared schema/tool-inputs.json and the get-llm-total-costs-for-project tool-schema snapshot from the Zod source (not hand-edited).

How did you test this code?

• Added an integration test case asserting the tool falls back to the active project when projectId is omitted (aiObservability.integration.test.ts).
• Regenerated schema/tool-inputs.json and the tool-schema snapshot with the repo's own generator + oxfmt so they match what CI produces; the resulting diffs are confined to this one schema (description added, projectId removed from required).
• I (an agent) could not run the full tsgo typecheck, oxfmt/oxlint across the whole package, or the live integration test here, since that needs a full monorepo install and live PostHog credentials. The change is type-safe by inspection: getProjectId() returns Promise<string> and String(params.projectId) is a string, matching context.api.query({ projectId }). Please let CI run these.

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Requested from a Slack thread and implemented by the PostHog Slack app (Claude). The fix was originally scoped against the archived posthog/mcp repo; on discovering the code now lives in this monorepo under services/mcp, I re-applied it here and regenerated the derived schema artifacts to match. No repo skills were invoked.

---

Created with PostHog from a Slack thread

[github-actions]

Hey @Radu-Raicea! 👋

It looks like your git author email on this PR isn't your @posthog.com address (radu@raicea.com). Since you're on the PostHog team, it's worth pointing your local git author email at your @posthog.com address. Why it matters:

• Consistent work identity in git history — internal tooling that attributes commits to team members keys off your @posthog.com address.
• Keeps team contributions easy to tell apart from external community ones when scanning history.

You can fix it for this repo with:

git config user.email "you@posthog.com"

Or set it globally with git config --global user.email "you@posthog.com". No need to redo this PR — just a nudge for next time. 🙂

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix(mcp): default get-llm-total-costs-fo..." | Re-trigger Greptile}

[stamphog]

Small, focused fix by an owning-team author with fresh familiarity in these paths; makes an MCP param optional with a type-consistent fallback matching the codebase convention, has test coverage, and a bot reviewer already signaled no concerns. Not risky territory.

• Author wrote 33% of the modified lines and has 16 merged PRs in these paths (familiarity MODERATE).
• 👍 on the PR from greptile-apps[bot], hex-security-app[bot].

Gate mechanics and policy version

Gate		Result
prerequisites	✓	all clear
deny-list	✓	no deny categories matched
size	✓	16L, 3F substantive, 25L/5F incl. docs/generated/snapshots — within ceiling
tier	✓	T1-agent / T1b-small (25L, 5F, single-area, fix)
stamphog 2.0.0b3		.stamphog/policy.yml @ 484770e · reviewed head ab8e3eb

[deployment-status-posthog]

Deploy status

Environment	Status	Deployed At	Workflow
dev	✅ Deployed	2026-07-24 18:25 UTC	Run
prod-us	✅ Deployed	2026-07-24 18:46 UTC	Run
prod-eu	✅ Deployed	2026-07-24 18:48 UTC	Run