[zackees]

Adds the canonical narrowed design-principles block from zackees/ci.yml docs/policy-rust.md ("Design principles, narrowed", forge-ci/ci.yml#163) to CLAUDE.md, the repo's agent doc, placed after the hard rules and before "Repo facts". Agent/review guidance only: no rule ID, not enforced by ci-lint. Docs-only (CLAUDE.md); no workflows, no code. The head is stamped by ci-lint local-gate run (45/45 checks, Local-Gate: trailer).

Adopted / adapted / dropped (forge-ci/ci.yml#163)

The block is the canonical text; "Adapted" means the wording was changed or bound to something this repo already has.

#	Baseline rule	Decision	Reason (this repo)
1	rg before adding a resolver/guard	Adopted	Applies to both the rust/ crates and the fork's src/profile*.c/memory-events files, where duplicating helpers next to upstream ones is the main drift risk.
2	Conflicts get a research issue	Adopted	Complements hard rule 7 ("escalate, don't improvise"): a design decision goes on an issue, not into an inline winner.
3	Behaviour and refactor in separate commits/PRs	Adapted	Cross-references hard rule 2 (never mix C-core and rust/ paths in one commit). Both rules apply.
4	Refactor first only past 50 lines into a >200-line function	Adapted	Adds that upstream mimalloc files are never restructured (hard rule 6: new logic in new files, a few guarded lines in upstream files). Without that, rule 4 could license extracting from an upstream function and break byte-identical overlay re-application.
5	Function/file size follow RUST-018	Adapted	rust/ has no clippy too_many_lines/cognitive_complexity config, so there is no ratchet and no #[expect]s. The directive keeps the 100/25 ceilings for new functions, says nothing mechanical holds them yet, and keeps the include! ban (zero fragments today).
6	Fail fast; delete before abstracting; no single-impl trait	Adapted	Bound to hard rule 7 (escalate on the issue rather than improvise a fallback). Matches the owner rule that observability defaults are named explicitly rather than relied on.
7	Existing boundaries over generic DRY	Adapted	The boundaries here are the upstream overlay (hard rules 2 and 6) and the rust/ crate split. This repo has no Dylints, so the Dylint clause names none.
--	"HARD RULE refactor first", composition over inheritance, Open/Closed	Dropped	Dropped fleet-wide by #163: refactor-first is contradicted by soldr's regression history (soldr#2559, soldr#1490); the other two are not meaningful in Rust.