P0: stand up executus harness module above majordomo

Batteries-included agent-harness base, extracted from mort's agent layer.
This first cut establishes the module + the zero-coupling core primitives:

- lane, dispatchguard, pendingattach, run/progress.go: moved verbatim from mort
- config: host config Source seam + env-var default (nil-safe helpers)
- deliver: output-egress seam + Discard/Stdout defaults
- identity: AdminPolicy + MemberResolver seams (nil-safe)
- fanout: programmatic N×M swarm (bounded global + per-key concurrency)
- README/CLAUDE.md with the vibe-coded banner; CI with Go gates +
  the "core stays majordomo+stdlib only" invariant

Core builds with stdlib only today; majordomo enters at P1 (model/structured).
go build/vet/test -race all green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -1,2 +1,61 @@
 # executus
 
+> ⚠️ **This project is vibe-coded.**
+> executus is written almost entirely by an AI coding agent (Claude), with a
+> human steering at the design and review level rather than typing the code.
+> That's a deliberate choice, stated up front — the same way [gadfly] is. Read
+> the code before you depend on it, pin a version, and file issues if something
+> looks off. It is offered as-is.
+
+[gadfly]: https://gitea.stevedudenhoeffer.com/steve/gadfly
+
+A **batteries-included base for building LLM agent harnesses in Go.** Import it,
+do a little wiring, and you have agentic capabilities: a bounded run loop, a tool
+registry with a suite of common tools, context compaction, config-driven model
+tiering and failover, structured output, and parallel fan-out — with sensible
+defaults so a brand-new project is agentic with almost no setup, and pluggable
+seams so a serious host can swap in its own storage, config, delivery, and tools.
+
+executus sits **strictly above** [majordomo] — the lean LLM substrate (agent
+loop, canonical `llm` types, providers, media normalization, model parsing /
+failover / tiering). majordomo stays the substrate; executus is the opinionated,
+batteries-included layer on top. executus requires **no changes to majordomo**.
+
+[majordomo]: https://gitea.stevedudenhoeffer.com/steve/majordomo
+
+## Status
+
+Early. Being extracted, phase by phase, from the agent layer of [mort] (a Discord
+bot) — mort and gadfly are the first two consumers (heavy and light). See
+`CLAUDE.md` for the architecture and the extraction roadmap (P0–P6).
+
+[mort]: https://gitea.stevedudenhoeffer.com/steve/mort
+
+**Available today (P0):**
+
+- `lane/` — bounded worker pool with fair-share queueing (run- and
+  provider-concurrency).
+- `fanout/` — programmatic N×M swarm with bounded global + per-key concurrency.
+- `config/` — the host config seam (`Source`) with an env-var default.
+- `deliver/` — the output-egress seam with `Discard`/`Stdout` defaults.
+- `identity/` — caller-identity seams (`AdminPolicy`, `MemberResolver`).
+- `dispatchguard/`, `pendingattach/`, `run/progress.go` — run-safety primitives.
+
+## Design
+
+Two tiers in one module (`go.mod` = majordomo + stdlib only):
+
+- **Core** — everything a light host needs to be agentic: run loop, tool
+  registry + common tools, model resolution, compaction, lanes, fan-out,
+  structured output. No persistence, no scheduling.
+- **Batteries** (opt-in sibling packages) — persona/agent nouns, saved skills,
+  audit, run-critic, scheduling, budgets, checkpointing. Each is nil-safe and
+  ships a default, so you add only what you use.
+
+Persistence that needs a real database lives in a **separate** nested module
+(`contrib/store`, pure-Go SQLite) so the core never drags in a DB driver — a
+static-binary host (gadfly) stays static.
+
+## License
+
+TBD.