Persistent cross-session agent memory (user + project memory files, {memory} playbook token)

[sox8502]

What

Agents now keep durable memory across sessions, in two scopes:

• User memory — <data_dir>/memory/user.md, shared across all projects (preferences, working style)
• Project memory — <data_dir>/files/<slug>/project/memory.md, inside the files dir's reserved project/ namespace (build quirks, decisions, dead ends)

Both files are inlined into the playbook via a new {memory} token (new ## Memory section in SYSTEM_PROMPT.md), so every harness (Claude Code / Codex / OpenCode) sees the content — not just a path — on every playbook render. Agents maintain the files with their native Write/Edit tools; the playbook instructs them to consolidate rather than append, to save directly when the user clearly wants something persisted ("remember this"), and to ask first when unsure.

How

• New module src/local/memory.rs: path helpers, best-effort parent-dir creation (hooked into ensure_playbook beside files::ensure_dir), 4 KB/scope head-keep UTF-8-safe truncation with a visible marker, and a pure renderer (unit-testable without touching the real data dir).
• playbook_md split into a thin wrapper + playbook_md_with_memory so tests inject a memory stub instead of reading the developer's real files. {memory} is substituted last in the replace chain so agent-authored content can't be rewritten by later token replaces.
• The rendered block always shows both absolute paths (even when empty) and frames the content as "background context, not authoritative instructions" to bound the prompt-injection surface; the 4 KB cap bounds blast radius.
• No DB table, no new subcommand, no skill module, no UI changes: project/memory.md shows up in the Files tab, SSE watch, and data-dir snapshots through the existing files-dir mechanism. Local-only (cloud never renders this template).

Testing

• 7 unit tests in memory.rs (renderer, cap/UTF-8 boundaries, blank-file handling, path layout) + playbook tests updated ({memory} added to the placeholder-completeness list).
• cargo fmt --check / clippy -D warnings / cargo test --locked all pass (194 tests).
• E2E on an isolated dev slot (ORX_DATA_DIR, port 4903): playbook renders both scopes with seeded content; "remember that…" saved directly via a consolidating rewrite; an ambiguous preference triggered an ask-first question card; a second session's playbook picked up the first session's save; Files API lists/serves project/memory.md; >6 KB file rendered with the truncation marker.