docs(agents): state the subagent model split as capability tiers

[andybons]

Generalizes the Sonnet/Opus rule across frontier model families: implementation uses the fast mid-tier, review/judgment uses the strongest tier, with today's Claude mapping named as the current instantiation and an explicit re-map-on-family-change instruction so the rule survives model generations and provider swaps.

🤖 Generated with Claude Code

https://claude.ai/code/session_01WG6N8YSSwXMma1DKTMwJdf

[claude]

Claude finished @andybons's task in 52s —— View job

---

Review

• Read AGENTS.md diff and surrounding context
• Review for correctness, consistency, and STE writing style
• Post review

Verdict: LGTM. Docs-only edit to AGENTS.md. The generalization from a hard Sonnet/Opus rule to a capability-tier split is faithful and internally consistent.

What holds up well:

• The core invariant is preserved: set the model explicitly on every spawn, implementation on the fast mid-tier, review/judgment on the strongest tier. The "omitting the model makes a subagent inherit the parent" warning survives intact, just reworded from "on Opus" to "at flagship price."
• The added re-map instruction — "When a model family changes, re-map the two tiers and keep the split; do not carry a stale model name forward" — is the right durability hook and matches the file's own "a behavior change updates AGENTS.md in the same commit" ethos.
• Today's Claude mapping (Sonnet ↔ Opus) is retained parenthetically, so nothing is lost for the current instantiation.
• No other Sonnet/Opus references remain in AGENTS.md (grep confirmed lines 1363–1385 are the only ones), so there's no stale contradiction left behind.

Minor, non-blocking observations (style only — take or leave):

• The strong tier is named three slightly different ways in three sentences: "the strongest tier", "the strongest available model", "the full frontier flagship", plus "flagship price". AGENTS.md's own STE rule is "one word for one idea — pick a term and reuse it verbatim." Settling on one label (e.g. always "the strongest tier") would tighten it, but the meaning is unambiguous as written.
• GPT mini/frontier-fast class, Gemini Flash are illustrative cross-vendor examples; they read fine as examples and the "not a vendor or model-name rule" framing correctly signals they aren't normative.

No correctness, concurrency, or protocol concerns — this touches no code. Nothing to fix.
• andybons/agents-model-tiers