Code Review: fix-context-sizing

Status: PASS

AI assistant (per user directive "i approve all tasks. drive them to completion")

scripts/vram_detect.py (350-line region) — recommend_context rewrite, main() extension with --loop-mode, JSON output additions
config.md — new ## Loop Role Models section
prompts/decompose.md — 4k tier added, 16k floor REFUSE line added
tests/test_context_sizing.py — 15 new tests
tests/test_vram_detect.py:76 — updated test_recommend_context_api_model to assert the corrected single-headroom contract

R1 (single headroom): PASS — recommend_context returns recommended_kb pre-headroom, max_peak_kb = net_kb * (100 - headroom_pct) // 100 (headroom exactly once). Confirmed by test_recommend_context_single_headroom.
R2 (no fake defaults): PASS — else 8 / else 6 fallbacks removed; max(0, ...) clamp removed. Warning emitted in non-loop mode when budget ≤ 0 or model unknown. Confirmed by test_no_fake_defaults_when_budget_zero, test_no_max_zero_clamp_in_output.
R3 (--loop-mode refuse): PASS — unknown model exits 2 ("model context window is unknown"); sub-floor budget check gated on LOOP_MODE_CONTEXT_FLOOR_KB == 16_000. User override is authoritative per existing _parse_config_model flow. Confirmed by test_loop_mode_refuses_unknown_model, test_loop_mode_passes_for_known_model.
R4 (JSON fields): PASS — available_context_kb, loop_mode_eligible, loop_mode present; available_context_kb == max_peak_context_kb. Confirmed by test_json_includes_available_context_kb_and_eligible.
R5 (config.md ## Loop Role Models): PASS — section added verbatim with role definitions, D12/D13 references. Confirmed by test_config_md_includes_loop_role_models_section.
R6 (decompose.md 4k tier + 16k floor): PASS — **4k VRAM** in guidelines, (4k VRAM) in size targets, ≤ 16k ... REFUSE floor line present. Confirmed by test_decompose_md_includes_4k_tier, test_decompose_md_includes_16k_floor_refuse.

New tests: 15 passed
Full suite: 264 passed (one pre-existing test updated to match fixed contract; no regression)
Pre-existing self-consistency suite: 74 passed (no regression to prompt path enforcement or framework invariants)

One pre-existing test (test_recommend_context_api_model) was asserting the bug. Updated to assert the fixed contract. Documented inline as the reason.
--loop-mode is opt-in via CLI flag. Non-loop callers preserve prior behavior + gain a human-readable warning. Backward-compatible.
The override-is-authoritative path (D13) was already honored by _parse_config_model; no new parsing code needed.

Ship. No defects blocking transition.