Cache Discord media locally

[Peyton-Spencer]

Summary

Cache Discord images locally while their signed CDN URLs are still valid, then render them through T3's existing signed local asset route. This is stacked directly on #5.

Changes

• validate Discord CDN hosts, redirects, response types, image signatures, and a 25 MiB size limit
• deduplicate downloads and store them atomically under deterministic local attachment ids
• clean only discord-* cache files after 30 days or above a 1 GiB LRU budget
• prefer signed local asset URLs in Inbox and show an exact-message Discord fallback for expired media
• store no Discord token, cookie, or browser credential

Recovery finding

Opening an exact Discord message produced a fresh signed URL transiently, but Discrawl v0.13.3's full wiretap later overwrote it with an older duplicate and a targeted fetch still returned HTTP 404. This PR therefore does not automate accessibility or hidden Discord navigation; expired media uses an explicit exact-message fallback until Discrawl can deterministically preserve the newest attachment URL.

Test plan

• pnpm --filter t3 typecheck
• pnpm --filter @t3tools/web typecheck
• pnpm --filter t3 exec vp test run src/channels/DiscordMediaCache.test.ts src/channels/DiscrawlAdapter.test.ts
• pnpm --filter @t3tools/web build
• pnpm exec vp check (0 errors; 19 pre-existing warnings)

Note

Add local Discord media cache to Discrawl channel adapter

• Introduces DiscordMediaCache in DiscordMediaCache.ts to download and store Discord image attachments on the local filesystem with host, expiry, type, signature, and size (<= 25 MiB) validation, atomic writes, deduplicated in-flight fetches, and a periodic sweeper that removes files older than 30 days and trims total cache to <= 1 GiB.
• Wires the cache into makeDiscrawlAdapter via ChannelRegistry.ts and DiscrawlAdapter.ts; listed messages now include cachedAttachmentId and cacheState on attachments when caching is enabled.
• Updates InboxPage.tsx with DiscordAttachment, CachedDiscordAttachment, DiscordImage, and DiscordAttachmentButton components that render locally cached assets via useAssetUrl, show an open-in-Discord button for expired links, and fall back to remote URLs otherwise.
• Extends ChannelAttachment in channels.ts with optional cachedAttachmentId and cacheState fields.
• Risk: DiscordMediaCache writes to config.attachmentsDir; incorrect config or a full disk will cause cache failures to surface as unavailable attachments rather than errors. Sweeper deletes any discord--prefixed files in the attachments directory older than 30 days, so existing files matching that pattern will be removed.

^{Macroscope summarized 2e710d1.}

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ No successful main baseline artifact is available yet. This run establishes the initial measurement.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	—	13.3 KiB	—	15.1 KiB	✅
Codex	Thread snapshot wire	—	6.9 KiB	—	7.3 KiB	✅
Codex	Live turn WebSocket wire	—	6.4 KiB	—	7.8 KiB	✅
Codex	Live turn WebSocket decoded	—	55.6 KiB	—	66.4 KiB	✅
Codex	Live turn messages	—	11	—	21	✅
Claude	Total thread wire	—	13.4 KiB	—	15.1 KiB	✅
Claude	Thread snapshot wire	—	6.9 KiB	—	7.3 KiB	✅
Claude	Live turn WebSocket wire	—	6.5 KiB	—	7.8 KiB	✅
Claude	Live turn WebSocket decoded	—	56.4 KiB	—	66.4 KiB	✅
Claude	Live turn messages	—	11	—	21	✅

Baseline: unavailable · PR result: 2e710d1 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 109.4 KiB
• Claude decoded thread snapshot: 110.1 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.