feat: agents read cross-tool instruction files at session start

AGENTS.md, CLAUDE.md, copilot-instructions.md, and .cursorrules may
contain project knowledge added by other tools or people. Agents now
read these files at session start and merge new knowledge into
.memory/knowledge.md as the canonical source.

.config/opencode/AGENTS.md

@@ -16,7 +16,7 @@ Use markdown files in `.memory/` as the persistent project memory across session
 
 **Workflow: read files → work → update files**
 
-1. **Session start:** Read `.memory/` directory contents and skim `.memory/knowledge.md`.
+1. **Session start:** Read `.memory/` directory contents and skim `.memory/knowledge.md`. Also check for cross-tool instruction files (`CLAUDE.md`, `.github/copilot-instructions.md`, `.cursorrules`) — they may contain project knowledge added by other tools.
 2. **Before each task:** Read relevant `.memory/*.md` files before reading source files for project understanding.
 3. **After each task:** Update the appropriate `.memory/*.md` files with what was built.
 
@@ -45,6 +45,7 @@ Be specific in summaries: include parameter names, defaults, file locations, and
 - When project knowledge changes significantly, update **all** cross-tool instruction files.
 - When initializing or bootstrapping a project, create **all** cross-tool instruction files.
 - Do not duplicate `.memory/` internals in these files; they describe how to work with the project, not project tracking state.
+- **Read existing instruction files** at session start or when joining a new project. Other tools/people may have added project knowledge to `CLAUDE.md` or `.cursorrules` that isn't yet in `.memory/`. Merge any new knowledge into `.memory/knowledge.md` as the canonical source.
 
 ## Session Continuity