feat: deepen 268 exploitation skills; web session delete; CSS design system; JEV progress checkpoint

agents_md (skills):
- enrich all 255 vulns/ + 13 chains/ agents from thin one-liner stages to
  concrete playbooks: exact tools/commands, per-stack decision points, benign
  proof markers (unique OOB nonces, single reads, URLDNS-before-exec), explicit
  proof criteria, false-positive/pitfall sections, and chaining hooks. Every
  contract preserved (## User/System Prompt, {target}/{recon_json}, FINDING
  block, CWE/Severity, credits). avg 37->53 lines; loader parses all 449.

web console:
- delete a session/report: DELETE /api/runs/:id and DELETE /api/runs (all),
  a Delete button in the run detail and a hover ✕ per sidebar row (tested e2e)
- CSS design system: tokenise the loose values into one scale — 8-step type
  scale (was 10 ad-hoc sizes), radius/z-index/motion/scrim/terminal tokens,
  fix an undefined var(--muted); 66 tokens, 0 loose font sizes, all var() resolve
- stale version labels 4.0.0/4.2.0 -> 4.2.1

harness (JEV / System One):
- typesafe::progress_checkpoint (jev-skill agent-checkpoint pattern:
  continue/pivot/stop) wired into the attack-chain loop to stop looping rounds
  early; works with TypeSafe or local Laya via from_env(); honours --typesafe off
- 390 tests passing

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

agents_md/vulns/byte_range_cache.md

@@ -8,16 +8,29 @@ You are testing **{target}** for Byte-range request cache poisoning.
 
 **METHODOLOGY:**
 
-### 1. Test range caching
-- Send range requests and inspect how the cache stores/serves partial content
+### 1. Test range caching (fingerprint the cache first)
+- Confirm a CDN/cache is in front: `Age`, `X-Cache`, `CF-Cache-Status`, `Via`, `X-Served-By` headers.
+- Send a range request: `curl -sI -H "Range: bytes=0-99" {target}/asset.js` — expect `206 Partial Content` + `Content-Range`.
+- Probe the cache key: does the cache store per-range or normalize to the full object? Send varied ranges and inspect `X-Cache`/`Age` to see hit/miss behaviour.
+- Malformed/edge ranges: `bytes=0-`, `bytes=-1`, `bytes=0-0,-1`, huge start, multipart `bytes=0-1,3-4`, overlapping ranges.
 
-### 2. Poison
-- Cause a partial/inconsistent entry to be cached under a shared key (controlled)
+### 2. Poison (controlled — a resource/key you can safely target)
+- Try to get a PARTIAL or inconsistent body cached under a key a normal (no-Range) request will hit: e.g. a 206/partial stored and later served to a full-object request, or a range-induced error page cached.
+- Vary only what the cache ignores in its key (unkeyed range handling) so a benign resource under your control becomes the poisoned entry — do not target shared production assets that would harm other users.
+- Use a unique nonce in the request/path so you can attribute the cached entry to this test.
 
 ### 3. Confirm
-- Show a normal request retrieves the corrupted cached content
+- After poisoning, make a NORMAL request (no Range header) to the same key and show it returns the corrupted/partial content (truncated body, wrong `Content-Length`, or the cached error).
+- PROOF = the poisoning request(s) + the subsequent clean request retrieving the corrupted cached body, with cache-hit headers (`Age`>0 / `X-Cache: HIT`).
+- Roll back / let the entry expire; note TTL.
 
-### 4. Report Format
+### 4. Pitfalls / false positives
+- A 206 to YOUR range request is normal — the finding is a NORMAL request getting corrupted content.
+- Cache correctly keying on Range (separate entries) = working; not a finding.
+- `Vary: Range` / origin re-validation defeats it — note the mitigating header.
+- Content that looks truncated but is a correct full small file — verify `Content-Length` mismatch.
+
+### 5. Report Format
 For each CONFIRMED finding:
 ```
 FINDING:
@@ -31,6 +44,7 @@ FINDING:
 - Impact: Cache serves corrupted/partial content to users
 - Remediation: Normalize range handling in cache, validate range/content consistency
 ```
+**Chaining hooks:** if a JS/HTML asset can be poisoned to truncate at a chosen boundary → potential script/DoM breakage or XSS via partial-response confusion; overlaps with request-smuggling/cache-deception surfaces.
 
 ## System Prompt
-You are a byte-range cache specialist. Report only when a normal request retrieves poisoned/corrupted cached content, evidenced. Respect ROE; no flooding.
+You are a byte-range cache specialist. Report only when a normal request retrieves poisoned/corrupted cached content, evidenced with cache-hit headers. Respect ROE; no flooding. Target only a benign resource/key under your control and use a nonce to attribute the entry — do not poison shared production assets in a way that harms other users; roll back or let the entry expire. A correctly keyed 206 or a `Vary: Range` cache is a working control, not a finding.