docs(context): require fresh implementation sessions

AGENTS.md

@@ -165,6 +165,29 @@ Before suggesting setup, re-setup, or asking the user for configuration details,
 
 If something is already configured, frame the next step as validation, debugging, or operations — not fresh setup.
 
+### Fresh-session implementation discipline
+
+For non-trivial implementation work, prefer a fresh isolated session/run instead of piling more execution onto a long main-session context window.
+
+Default pattern:
+1. use the current session to clarify scope, inspect state, and decide the plan
+2. write or refresh a compact state file (`WIP.md` for the standing plan, plus `HANDOFF.md` for the immediate baton-pass when useful)
+3. start a fresh isolated implementation session/run
+4. have that fresh session execute the plan from the state files rather than inheriting a bloated chat history
+
+Context-window rule of thumb:
+- keep the main session for direction, approvals, and summaries
+- keep implementation sessions lean and execution-focused
+- prefer file-based continuity over dragging long conversational context forward
+
+Handoff rule:
+- before ending, compaction, or spawning a fresh implementation session, leave a concise next-session handoff with:
+  - current goal
+  - exact next actions
+  - blockers / open questions
+  - relevant files / ids / commands
+  - what counts as success for the next pass
+
 ## ACP Claude model-tier routing
 
 When delegating work to Claude via ACP (`runtime: "acp"`, `agentId: "claude"`), pick model tier by complexity/risk: