feat(miner-ui): useStreamingText hook + StreamingText renderer

[jaytbarimbao-collab]

Summary

The first streaming-text primitive for the miner-ui chat rail (#6516): progressively reveal a chat response's text as chunks arrive. Unwired plumbing only — no backend, no route, no live fetch/EventSource; exercised solely against mock chunk sources in tests.

Deliverables

• lib/use-streaming-text.ts — useStreamingText(source) consumes a ChunkSource (a () => AsyncIterable<string> factory, exported by name for a future composer/message-list to type against), accumulating each chunk into text with an idle | streaming | done | error | cancelled status and a cancel(). Mirrors usePolledFetch's cancelled-flag discipline: a chunk resolving after a new source starts, after cancel(), or after unmount never touches state; a mid-stream throw/reject surfaces via status/error, never as an unhandled rejection.
• components/streaming-text.tsx — thin <StreamingText> renderer showing the accumulated text with a caret while streaming, suppressed under prefers-reduced-motion (detected via window.matchMedia + a change listener — the use-mobile.tsx technique; no motion dependency added).
• use-streaming-text.test.ts + streaming-text.test.tsx — co-located flat in src/, mirroring use-polled-fetch.test.ts.

Tests (every branch)

Incremental accumulation across renders; cancel-on-new-source (late chunk from the abandoned source ignored); cancel-on-unmount (no late state write, no throw); mid-stream error → status: error; renderer full-motion caret vs reduced-motion suppression + final text. apps/** is Codecov-ignored, so the operative gate is the local vitest coverage threshold (85/85/75/85) — this PR lands the suite at 88/86/81/90. Local @loopover/ui-miner typecheck + 192 tests + eslint (0 errors) all green.

Closes #6516

[superagent-security]

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

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Caution

🛑 LoopOver review result - fixes required

_{Review updated: 2026-07-16 14:50:33 UTC}

4 files · no blockers · CI failing · blocked

🛑 Suggested Action - Fix Blockers

• AI review already in progress for this PR head: Another LoopOver pass is already running the AI review for this exact PR head. This pass is skipping to avoid a duplicate LLM call.

Review summary
AI review is already running for this PR head in another LoopOver pass. LoopOver is holding this PR for manual review until that pass completes.

Nits — 1 non-blocking

• AI review already in progress for this PR head — The gate is held for a human reviewer rather than passed automatically; it re-evaluates once the in-flight review completes or on the next update.

CI checks failing

• validate
• validate-code

Decision drivers

• ✅ Code review — No blockers (No AI review summary)
• ⚠️ Gate result — Not blocking (Advisory; not blocking this PR.)

Context & advisory signals — never blocks the verdict

Signal	Result	Evidence
Linked issue	✅ Linked	#6516
Related work	⚠️ 2 scoped overlaps	Top overlaps are listed below; lower-confidence bulk is hidden.
Change scope	❌ 8/20	High 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: 148 registered-repo PR(s), 78 merged, 4 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	jaytbarimbao-collab; Gittensor profile; 148 PR(s), 4 issue(s).
Improvement	✅ Minor	risk: clean · value: minor

Review context

• Author: jaytbarimbao-collab
• Role context: outside_contributor
• Public audience mode: oss maintainer
• Lane context: Repository is configured for direct PR review.
• Public profile languages: Rust
• Official Gittensor activity: 148 PR(s), 4 issue(s).
• Related work: Titles/paths share 7 meaningful terms. (issue #6516, issue #6518)
• Related work: Titles/paths share 6 meaningful terms. (issue #6516, issue #6303)

Contributor next steps

• Start here: Review top overlaps.
• Then work through the remaining 2 steps in the Signals table above.

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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