feat(clickhouse): exercise the declarative schema canary

[rorylshanks]

Problem

Operators can verify one real schema change through the reviewed-plan deployment flow.

Changes

Changes only the help string in custom_metrics_test; metric names, values, labels and query shape stay the same.

Rollout gate: Merge only after infra canary adoption has completed. Dispatch the merged catalogue commit, approve the one-view update, apply it, verify the metric and require an empty subsequent plan. Merge bottom-first; do not land the whole stack together.

Before:

flowchart LR
  A["Adopted view"] --> B["Existing help text"]
  classDef phBlue fill:#1d4aff,stroke:#1d4aff,color:#fff;
  classDef phGray fill:#e5e7eb,stroke:#c7ccd1,color:#000;
  class A phBlue;
  class B phGray;

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After:

flowchart LR
  A["Reviewed view update"] --> B["Updated help text"]
  classDef phBlue fill:#1d4aff,stroke:#1d4aff,color:#fff;
  classDef phGray fill:#e5e7eb,stroke:#c7ccd1,color:#000;
  class A phBlue;
  class B phGray;

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How did you test this code?

Local catalogue validation and table-family checks passed, including the empty second plan. posthog/clickhouse/test/test_managed_schema.py --reuse-db passed against local services. Python lint/format, lockfile and workflow checks passed. Live cloud rollout, the complete backend suite and both events-schema variants remain CI/review gates.

Test rationale: The existing schema validator covers view syntax; a separate test of a literal help string would duplicate the change. The real rollout is verified through the canary plan, apply and subsequent empty plan.

Release status

• No feature flag controls this change
• This change is behind a feature flag and is not available to users
• This change makes a previously flagged feature available to everyone

Automatic notifications

• Publish to changelog?

Docs update

No additional documentation is needed for the help-string-only canary.

🤖 Agent context

Autonomy: Human-driven (agent-assisted). Agent: Codex, GPT-6.

Staged replacement for #109937, which remains available for comparison. Source changes were split using Git, GitHub CLI and gh stack; current master changes were retained. Skills: /stacking-prs, /writing-pr-descriptions, /running-ci-preflight, /authoring-ci-workflows, /clickhouse-migrations, /writing-tests, /writing-code-comments and /reviewing-with-coderabbit. Local CodeRabbit review was skipped at the directing user's request because the CLI was missing. No customer material was used. Human review and CI patch coverage are pending on this draft.

[github-actions]

🤖 CI report

🚨 Trunk lane — universal lane

This PR is assigned to the universal lane. It cannot merge in parallel with other PRs, so it can take longer to merge. Ask dev-ex if you think this is wrong.

[greptile-apps]

[Low risk] Updates a test metric description string.

The PR appears safe to merge after its stated infra adoption and reviewed-plan rollout gates are satisfied.

_{Reviews (1) · Last reviewed commit: "feat(clickhouse): exercise the declarati..."}

[coderabbitai]

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🧰 Additional context used

📚 Code guidelines (3)

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository: PostHog/posthog/.coderabbit.yaml

Review profile: QUIET

Plan: Enterprise

Run ID: b222b992-7d85-4eb1-a9b0-695c2110fa24

📥 Commits

Reviewing files that changed from the base of the PR and between c1bde28 and 4dcb77a.

📒 Files selected for processing (1)

• posthog/clickhouse/schema/catalog/custom_metrics/main.tf

Included review availability: This review used your included allowance. Your plan provides up to 12 included reviews per hour; 9 remain after this review.

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📝 Walkthrough

Walkthrough

The test custom metric’s help text now says that it checks whether the ClickHouse metric endpoint is working.

Priority: ⬇️ Low

Severity of issue fixed: Low

Merge Risk: ⚪ Minimal · up to 4dcb7

This updates only the test metric’s description; no PR-specific runtime or compatibility risk is evident.

Architecture Summary

Architecture risk: 🔵 Low · up to 4dcb7

The change affects 1 system.

Changed systems: posthog

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — posthog (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

• observed — Modified behavior in posthog/clickhouse/schema/catalog/custom_metrics/main.tf: Changed the test metric’s help text from “Test to check that the metric endpoint is working” to “Checks that the ClickHouse metric endpoint is working.”

🚥 Pre-merge checks | ✅ 1

✅ Passed checks (1 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description covers the problem, visible change, rollout plan, testing, test rationale, release status, documentation, and agent context. It is self-contained and appropriate for the small diff. So…

✨ Finishing Touches 💡 1

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