fix(selfhost): consume the injected central PostHog key as a POSTHOG_API_KEY fallback

[xfodev]

Summary

The hosted control-plane injects a fleet-wide LOOPOVER_CENTRAL_POSTHOG_KEY into each tenant container so the self-host image reports errors to the loopover-owned PostHog project. But initPostHog() in src/selfhost/posthog.ts only ever read POSTHOG_API_KEY — so the injected central key was never consumed, and hosted tenant containers reported to nothing.

• initPostHog() now resolves the key as processEnvString(env, "POSTHOG_API_KEY") ?? processEnvString(env, "LOOPOVER_CENTRAL_POSTHOG_KEY"): the operator's own POSTHOG_API_KEY keeps highest precedence (unchanged), and the hosted-injected central key is used only as a fallback when POSTHOG_API_KEY is unset — a hosted-image fallback, never a silent override of an operator's explicit config.
• When neither var is set, initPostHog still returns false and stays a complete no-op — self-host's existing opt-in behavior is unchanged.
• The module's self-host env-var header block is updated to name LOOPOVER_CENTRAL_POSTHOG_KEY as a fallback source alongside POSTHOG_API_KEY.
• Consumer-side fix only — the control-plane injection side is already correct and out of scope (its tests are left passing unmodified).

Tests

test/unit/selfhost-posthog.test.ts (82 pass, +3): the central key activates the client when POSTHOG_API_KEY is unset (asserts the client is constructed with the central key); POSTHOG_API_KEY still wins when both are set (client uses the operator key, never the central one); neither-set stays a no-op (false, client never constructed). These are the exact regression guards against an injected-but-never-consumed env var recurring — both branches of the new fallback covered.

Validation

• selfhost-posthog test file green (82); tsc clean on the changed file.
• No behavior change when neither var is set; operator POSTHOG_API_KEY precedence preserved.
• No secret/wallet/hotkey/trust/reward terms; control-plane injection side untouched.

Closes #8626

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.61%. Comparing base (b471ee1) to head (1034189).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8635      +/-   ##
==========================================
- Coverage   92.77%   90.61%   -2.16%     
==========================================
  Files         798       97     -701     
  Lines       79464    22642   -56822     
  Branches    24078     3947   -20131     
==========================================
- Hits        73725    20518   -53207     
+ Misses       4592     1945    -2647     
+ Partials     1147      179     -968     

Flag	Coverage Δ
backend	99.34% <100.00%> (+5.68%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/selfhost/posthog.ts	99.34% <100.00%> (ø)

... and 701 files with indirect coverage changes

[loopover-orb]

Tip

✅ LoopOver review result - approve/merge recommended

_{Review updated: 2026-07-25 16:10:59 UTC}

2 files · 1 AI reviewer · no blockers · readiness 100/100 · CI green · clean

✅ Suggested Action - Approve/Merge

• safe to merge

Review summary
This is a small, correctly-scoped fix: initPostHog() now falls back to LOOPOVER_CENTRAL_POSTHOG_KEY when POSTHOG_API_KEY is unset, preserving operator-key precedence and the existing no-op-when-neither-set behavior. The change is minimal, well-commented, and the diff maps cleanly to the stated bug (injected central key was never consumed). Test coverage directly exercises both branches of the new fallback (`??`) plus the neither-set no-op path, so the new logic is well-guarded.

Nits — 3 non-blocking

• The comment block above initPostHog references `control-plane/src/container-driver.ts` as the injection site (src/selfhost/posthog.ts:138) — worth double-checking that path is still accurate/exists, since a stale cross-repo/cross-file reference in a comment is easy to drift.
• LOOPOVER_CENTRAL_POSTHOG_KEY is read via `processEnvString` which trims blank/whitespace-only values to undefined, but there's no explicit test for a blank central key falling through to no-op the way there is for POSTHOG_API_KEY — minor asymmetry in test coverage.
• Consider adding one more test case mirroring the existing 'blank/whitespace POSTHOG_API_KEY' test but for LOOPOVER_CENTRAL_POSTHOG_KEY, for full symmetry.

Decision drivers

• ✅ Code review — No blockers (1 reviewer)
• ✅ Gate result — Passing (No configured blocker found.)

Context & advisory signals — never blocks the verdict

Signal	Result	Evidence
Linked issue	✅ Linked	#8626
Related work	✅ No active overlap found	No same-issue or scoped active PR overlap found.
Change scope	✅ 20/20	Low review scope from cached public metadata (1 linked issue).
Validation posture	✅ 25/25	PR body includes validation/test evidence.
Contributor workload	✅ 10/10	Author activity: 56 registered-repo PR(s), 23 merged, 0 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	xfodev; Gittensor profile; 56 PR(s), 0 issue(s).
Improvement	✅ Minor	risk: clean · value: minor · LLM: moderate

Linked issue satisfaction

Addressed
The diff implements the exact fallback (POSTHOG_API_KEY ?? LOOPOVER_CENTRAL_POSTHOG_KEY) requested, adds all three required regression tests (fallback activation, operator precedence, no-op when neither set), and updates the header comment block to document the new fallback var as required.

Review context

• Author: xfodev
• Role context: outside_contributor
• Public audience mode: oss maintainer
• Lane context: Repository is configured for direct PR review.
• Public profile languages: JavaScript, TypeScript
• Official Gittensor activity: 56 PR(s), 0 issue(s).
• PR-specific overlap: none found.

Contributor next steps

• Keep the PR focused and include validation evidence before maintainer review.

Signal definitions

• Related work = same linked issue, overlapping active PRs, or title/path similarity.
• Change scope = cached public metadata such as size labels, draft state, and review-burden hints.
• Validation posture = whether the PR provides enough public validation/test evidence for maintainer review.
• Contributor workload = public contributor activity and cleanup pressure, not a repo-wide quality failure.
• Contributor context = public GitHub/Gittensor identity context; non-Gittensor status is not a blocker.

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_{🟩 Safe / merged · 🟦 Advisory · 🟨 Held for review · 🟥 Blocked / closed}

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LoopOver approves — the gate is satisfied and CI is green.