test(miner-ui): add unit coverage for chat-scroll stick-to-bottom logic

[shin-core]

What & why

Closes #7793.

apps/loopover-miner-ui/src/lib/chat-scroll.ts (isChatViewportNearBottom, scrollChatViewportToBottom, CHAT_NEAR_BOTTOM_PX) encodes the boundary threshold and clamp math for the chat stick-to-bottom auto-scroll — fiddly logic that already needed a dedicated bug-fix once (#7229/#7298). No test exercised it directly: message-list.test.tsx only checks DOM structure/StateBoundary branches, and jsdom doesn't meaningfully simulate scrollTop/scrollHeight there. This closes that gap, following the one-test-per-pure-module convention demo-data.test.ts establishes in the same directory.

What's tested (a co-located chat-scroll.test.ts)

• isChatViewportNearBottom: distance 0 (at bottom); exactly at the 80px boundary (<= 80 → true) and one pixel past it (81 > 80 → false) — the both-sides boundary case that motivated the prior bug-fix; scrolled well up → false; short content (viewport taller than content, negative distance) → true; a custom threshold overriding the default (proving the arg is used); and that CHAT_NEAR_BOTTOM_PX === 80.
• scrollChatViewportToBottom: sets scrollTop to scrollHeight - clientHeight for scrollable content, and the Math.max(0, …) clamp pinning it to 0 when content is shorter than the viewport.

Pure coverage addition — no source change. Per the issue, apps/loopover-miner-ui is not under the src/** 99% patch gate; this new test file is the issue's own coverage deliverable.

Validation

• apps/loopover-miner-ui vitest run: 9 tests pass; tsc --noEmit exit 0; eslint clean; Prettier clean.
• Tests genuinely bite: mutating the boundary (<= → <) and dropping the Math.max(0, …) clamp each fail a test.
• New file only; branched off current main, mergeable-clean.

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

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Warning

⏸️ LoopOver review result - manual review recommended

_{Review updated: 2026-07-21 15:08:15 UTC}

1 file · 1 AI reviewer · no blockers · CI green · unstable

⏸️ Suggested Action - Manual Review

Review summary
This is a pure, additive test file for the already-existing `chat-scroll.ts` module, closing the coverage gap noted in issue #7793 with no production code changes. The boundary-condition tests (80px inclusive vs 81px exclusive) and the `Math.max(0, ...)` clamp test correctly mirror the actual implementation shown in the reference file, and the assertions match the real math rather than a fabricated scenario. This is a low-risk, well-scoped test-only PR that directly closes its linked issue.

Nits — 3 non-blocking

• The `viewport()` helper and file-level comment duplicate explanation already present inline per-test; could trim one or the other for brevity.
• Consider also testing a fractional/negative custom threshold edge case, though the current coverage of the core boundary is sufficient.
• No changes required; optionally add a one-line test asserting `scrollChatViewportToBottom` is a no-op when scrollTop already equals the target, though this is not required for coverage.

Flagged checks (non-blocking)

• Contributor trust — Contributor flagged for review

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	#7793
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: 90 registered-repo PR(s), 50 merged, 0 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	shin-core; Gittensor profile; 90 PR(s), 0 issue(s).
Improvement	ℹ️ Insufficient signal	risk: clean · value: insufficient-signal

Linked issue satisfaction

Addressed
The PR adds a co-located chat-scroll.test.ts directly exercising isChatViewportNearBottom (including both sides of the 80px boundary, custom threshold, and short-content cases) and scrollChatViewportToBottom's clamp behavior, matching the one-test-per-pure-module convention the issue asks for.

Review context

• Author: shin-core
• Role context: outside_contributor
• Public audience mode: oss maintainer
• Lane context: Repository is configured for direct PR review.
• Public profile languages: TypeScript, JavaScript, Solidity, Dart, Python, CSS, PHP, Rust
• Official Gittensor activity: 90 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.