♻️ Simplify PostHog telemetry configuration

[Vivekyy]

Summary

Removes the legacy POSTHOG_API_KEY fallback so runtime telemetry accepts POSTHOG_PROJECT_TOKEN or the release-embedded project token.

Keeps built-in host values empty unless a release explicitly configures POSTHOG_HOST, while preserving the US endpoint as the runtime default.

Adds Rudder-tagged integration coverage for supported tokens, rejected legacy keys, and release host generation.

Validation: npm run check:agent-layout, npm run typecheck, npm test (30 passing), and npm run build.

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Greptile Summary

Simplifies PostHog telemetry configuration.

• Removes support for the legacy POSTHOG_API_KEY runtime fallback.
• Leaves release-embedded hosts empty when no explicit host is configured and preserves the US runtime fallback.
• Adds integration coverage for project tokens, rejected legacy keys, and generated release-host behavior.

Confidence Score: 4/5

The PR appears safe to merge, with only non-blocking telemetry documentation drift to address.

Runtime and release behavior are consistently covered, but two repository configuration references still instruct maintainers to use the removed POSTHOG_API_KEY fallback.

Files Needing Attention: src/telemetry.ts and the telemetry almanac references

Important Files Changed

Filename	Overview
src/telemetry.ts	Removes the legacy token fallback while preserving embedded-token and runtime-host fallback behavior; related configuration references remain stale.
.github/workflows/publish.yml	Embeds an empty release host when POSTHOG_HOST is unset, allowing the bundled runtime fallback to select the US endpoint.
src/telemetry-build-config.ts	Changes the source-build host default to empty while keeping source-build telemetry disabled through the empty token.
test/prompt-hook.test.ts	Covers supported project-token telemetry, intentional rejection of the legacy API key, and release-embedded configuration.
test/plugin-package.test.ts	Adds static coverage for release host generation and the retained runtime default.

_{Reviews (1): Last reviewed commit: "♻️ Simplify PostHog telemetry configurat..." | Re-trigger Greptile}

Greptile also left 1 inline comment on this PR.

[ghost]

Ready to review this PR? Stage has broken it down into 3 individual chapters for you:

	Title
1	Simplify PostHog configuration and remove legacy fallback
2	Update release workflow for explicit host configuration
3	Verify telemetry configuration and legacy key rejection

_{Chapters generated by Stage for commit 18946c2 on Jul 30, 2026 2:54pm UTC.}

[github-actions]

📦 No plugin release on merge

The plugin package, tag, and GitHub Release already exist for 0.1.3.
Bump package.json to release a new plugin version.

[greptile-apps]

Legacy token documentation is stale

The token selection no longer reads POSTHOG_API_KEY, but the telemetry configuration references still document it as a supported fallback. Maintainers following those references will configure a key that leaves telemetry disabled, so the affected almanac pages should be updated alongside this change.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!