Add round-3 handover doc for the LLM test project

Covers the #014-#016 fixes (sanitization+CSP, nested-JSON 400, ragged-CSV
normalization) and flags the sanitizer as the top round-4 adversarial
target (mutation XSS, attribute/scheme bypasses, CSP presence). Notes #017
is a design issue, not a bug to re-report, and the aesthetic/UI changes
have no API surface.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

issues/018-handover-to-llm-test-round-3.md

@@ -0,0 +1,93 @@
+# 018 — Handover to AGENT_DAYBOOK__LLM_TEST (round 3)
+
+**Status:** For information — a handback covering everything fixed/changed
+since the round-2 handoff (#013).
+
+Round-2 testing (against #013's suggestions) filed #014, #015, #016 — all
+now fixed. This round-3 handoff summarizes those fixes and points at where
+the fresh adversarial surface is, plus one new design issue (#017) that is
+**not** a bug and shouldn't be re-reported.
+
+All changes are on `main` (pushed to Forgejo) and live on the local dev
+instance (`http://127.0.0.1:8001`) via autoreload — no restart needed.
+Test as always with the `test` / `testpwd` account and clean up after
+yourself.
+
+## Fixes since #013 (issues you filed)
+
+- **#014 (High) — stored XSS.** `markdown`, `html_fragment`, and `deck` are
+  now allowlist-sanitized (nh3) at create time: `<script>`, `on*` handlers,
+  `<style>`, and `javascript:`/`data:` URLs are stripped, while formatting/
+  tables/links/images (incl. relative `/assets/<id>`) survive. Those kinds
+  are also served with `Content-Security-Policy: script-src 'none'` (on both
+  `/a/{id}` and the public `/s/{token}` route). `html_full` is deliberately
+  **not** sanitized (verbatim escape hatch) and `json`/`csv` keep their
+  existing `escape_script_body` defense.
+- **#015 (Med) — deeply nested JSON → 500.** Now returns `400` on both
+  paths: the `json`-kind validator catches `RecursionError`, and a new DRF
+  `EXCEPTION_HANDLER` maps parser-level `RecursionError` (deep nesting
+  anywhere in the request body) to `400`.
+- **#016 (Low-Med) — ragged CSV rows.** `wrap_csv_viewer` now normalizes
+  every row to the max width (long rows widen the columns with auto-named
+  `Column N`; short rows pad with `""`), so no cell is dropped.
+
+## Other changes (context, mostly not API-surface)
+
+- Document artifact backgrounds unified to one off-white (`#faf9f6`) across
+  markdown/html_fragment/json/csv (report/tasks/base themes). Deck stays
+  dark; html_full/pdf unchanged. Only relevant to you as: the rendered HTML
+  background value changed — no behavioral/API change.
+- UI-only work (dark mode toggle, top-bar logo, sidebar width behavior,
+  greyscale chrome). No API surface.
+- **#017 filed — customizable theme variants.** A *design issue* (feature
+  request), not a bug. Don't re-report theme/color inflexibility as a bug;
+  it's tracked.
+
+## Suggested Round-4 Probes
+
+Prioritized by where the new surface is riskiest.
+
+### The sanitizer (#014) — now the top adversarial target
+
+The XSS fix is an allowlist sanitizer; the classic follow-up is trying to
+get past it. Worth hard probing on `markdown`, `html_fragment`, `deck`:
+
+- **Mutation/parser-confusion XSS**: malformed nesting, stray `<`/`>`,
+  comments (`<!-- -->`), CDATA, `<svg>`/`<math>` foreign-content vectors,
+  `<noscript>`/`<template>`, deprecated/odd tags — anything that might
+  re-parse into script after nh3 serializes.
+- **Attribute vectors**: `on*` variants, `style=` (should be stripped),
+  `href`/`src` with `javascript:`, `data:`, `vbscript:`, whitespace/newline/
+  encoding tricks (`java\tscript:`, `&#106;avascript:`), `srcset`, `formaction`.
+- **Allowlisted-tag abuse**: does anything survive on the *permitted* tags
+  (a/img/etc.) that shouldn't — e.g. `<a href>` protocol bypasses, `<img
+  src>` with odd schemes?
+- **CSP presence**: confirm `script-src 'none'` is actually on the response
+  for markdown/deck/html_fragment (both `/a/` and `/s/`), and absent for
+  html_full and json/csv. Confirm markdown/deck/html_fragment pages contain
+  no executable inline script at all after sanitization.
+- **html_full is out of scope** — it's verbatim by design; a `<script>`
+  surviving there is not a bug (documented). Don't file it.
+- Verify the sanitizer didn't over-strip: tables, code highlighting, links,
+  relative `/assets` images, headings/lists still render.
+
+### #015 recursion — other sites
+
+- Deeply nested `metadata` / `tag_colors` (string-parsed JSON), deeply
+  nested arrays vs objects, right-at-the-limit depths. Confirm 400 not 500.
+
+### #016 CSV — other raggedness
+
+- Header shorter than data rows, entirely empty first row, mixed quoting
+  with ragged widths, a row that's all empty cells. Confirm no data lost and
+  the auto-named columns behave.
+
+### Regression sweep
+
+- Re-run the #002–#012 repros briefly to confirm none regressed (esp. the
+  #010 quota race and #006 eviction, which have thin/no automated coverage).
+
+As always: use `test`/`testpwd`, clean up, check `artifacts/views.py` before
+calling a surprise a bug (some behavior is documented/by-design), and file
+anything real as a new numbered issue (next is #019), linking back if it's
+a variant of a closed one.