docs(citadel): record cover letter in session file

The session update in f8b4cd3 silently failed - the heredoc ran from a
stale working directory left by an earlier cd, so the commit landed
without it. Output Files and Cover Letter status now recorded.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MHtzyTKBcg6BWhD5qFegtK

output/CitadelSecurities_PlatformEngineer/session_citadel_securities_platform_engineer.md

@@ -241,6 +241,7 @@ or quoting any PnL, Sharpe, return or backtest figure.
 ## Output Files
 
 - `e2e_citadel_securities_platform_engineer_resume.tex` / `.pdf` — 2 pages, 13 bullets
+- `e2e_citadel_securities_platform_engineer_cover_letter.tex` / `.pdf` — 1 page, 270 words, 3 paragraphs
 - `resume.cls` (copied from templates)
 - `JD_CitadelSecurities_PlatformEngineer.txt` — verbatim posting
 
@@ -312,7 +313,10 @@ not a re-scored critique.
 - Phase 0: **DONE** (2026-08-25)
 - Phase 1: **DONE** (2026-08-26) — 13 bullets confirmed
 - Phase 2: **DONE** (2026-08-26) — resume compiled and verified
-- Cover Letter: **PENDING** (decision YES — PP-1 domain story needs prose)
+- Cover Letter: **DONE** (2026-08-26) — 1 page, 270 words, 3 paragraphs, validator PASS.
+  No external hooks by design (`cl_reference.md`: omit an unnecessary hook); the only hook is the
+  JD's own first-party language. States the R1 gap plainly rather than hiding it. PP-1 labelled
+  personal with an explicit "I make no claims for its results".
 - Critique: **STALE** (scored 86/100 on 2026-08-26, before Edit 1) — **Document Quality 86/100**, Evidence Fit 71, Channel Weak.
   No Tier 1 truth findings; validator PASS. Three Tier 1 relevance fixes (~+4), all honestly
   available: (1) R2's own vocabulary — ingestion/transformation/storage/lifecycle — is absent