docs: organize agent instructions

[BrianBland]

Group repository guidance by concern and clarify behavioral testing expectations so coding agents can apply the rules more reliably.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[depot-code-access]

✅ All benchmarks green — 14 within ±2% (deterministic instruction counts). View run

Benchmark details (14)

Benchmark	Base (target)	Head (this PR)	Δ instructions
batch_queue/drain/drain_cached_span_batches	242,027	242,027	+0.0%
batch_transaction/encode_in_place/encode_in_place	4,199,759	4,199,759	+0.0%
batch_transaction/temporary_frame_buffers/temporary_frame_buffers	8,408,350	8,408,350	+0.0%
flashblock_decode/decode/brotli	3,296,484	3,296,484	+0.0%
flashblock_decode/decode/plain_json	2,280,194	2,280,194	+0.0%
flz/compress_len/real_contract_call	43,148	43,148	+0.0%
flz/compress_len/synthetic_0	38,205	38,205	+0.0%
flz/compress_len/synthetic_1	54,682	54,682	+0.0%
flz/compress_len/synthetic_2	147,976	147,976	+0.0%
flz/data_gas	43,059	43,059	+0.0%
flz/tx_estimated_size	43,056	43,056	+0.0%
frame_parse/decode/single_4kib	1,031	1,031	+0.0%
frame_parse/parse_frames/few_large	1,053,062	1,053,062	+0.0%
frame_parse/parse_frames/many_small	154,763	154,763	+0.0%

[github-actions]

No findings. This is a documentation-only change that reorganizes existing agent instructions into structured sections with headers and bullet points. The content is substantively preserved, with minor wording improvements and a helpful expansion of the Testing section (behavioral testing expectations, change-detector test guidance). No code changes to review.

[depot-code-access]

Base Std historical fork tests

Fork	Result	Passed	Failed	Skipped	base/base	base-anvil	base-std
Beryl	pass	616	0	13	16942597	cecddfa5	4658f1b7
Cobalt	pass	721	0	14	16942597	fb00db40	e30b3421

View run