docs: record B5b upload-hardening scoping (register #50)

[tornidomaroc-web]

What

Docs-only. Creates docs/b5b-scoping.md — the B5b (deep upload content hardening) decision record — and logs it as register #50 in docs/PROGRESS.md. Scoping is not progress on the gate: the §1 B5b row (line 86) stays ⬜ and Phase 7 stays ⬜.

The scoping doc records

Established constraints (each verified against the code this session):

• The real upload ceiling is Vercel's hard ~4.5 MB edge cap (platform constant, 413 FUNCTION_PAYLOAD_TOO_LARGE before the handler) — not the 50 MB the app promises in 7 places (route.ts:51/:52, DropZone.tsx:26, four i18n strings; :52's message is hardcoded English, register-docs: record live-DB reconciliation + "migration ≠ applied" lesson #17 class).
• Ingestion runs on Railway (INGESTION_SERVICE_URL), so the route.ts→/convert hop faces no second Vercel cap but a 9–13× return-path blob (each chunk's 1024-float embedding inline + full markdown, materialized by await pyResponse.json()).
• No maxDuration anywhere (grep-empty) → the true user-facing ceiling is an UNMEASURED duration limit, not size.

Corrections recorded so they are not re-inherited:

• The 4.5 MB cap does not mitigate decompression bombs (bounds compressed bytes, never the expansion).
• The pre-auth body-buffering concern is bounded by the edge cap → the getUser-above-formData reorder is a low-priority ride-along (checkDocumentLimit can't move — needs kbId; enforceLimit shouldn't — it would burn a credit on a rejected request).
• PIVOT_PLAN.md:269's "Size cap (50 MB) already exists" is FALSE — corrected here; PIVOT_PLAN.md untouched.

The split: B5b-1 (request-path, doable now) vs. B5b-2 (gated on B6), plus enablers (b1) persist chunks from Railway and (b2) signed-URL direct-to-storage.

Seven OPEN founder decisions (stated with consequences, none picked) + one OUTSTANDING duration measurement (plain-.txt-on-Preview procedure + failure-signature table).

Scope

Only two files: docs/b5b-scoping.md (new) and docs/PROGRESS.md (register row #50, one append-only §7 block, three header lines). No code, no route/validation/size-constant change; PIVOT_PLAN.md untouched; register #17 stays OPEN.

Checks

• tsc --noEmit: pass (exit 0) — no .ts touched.
• db-types: unaffected — no supabase/migrations/** or database.types.ts touched.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated (UTC)
knowflow	Ready	Preview, Comment	Jul 23, 2026 6:51pm