docs: adopt dependencies-over-hand-rolling policy from NIH audit

A repo-wide Not Invented Here audit (ten parallel domain surveys covering
every package group, scripts/, native/, vendor/ edges, python/, test
infrastructure, and CI) asked of each hand-rolled surface whether a
maintained external package or Node builtin deletes it with a net win.

Policy: new implemented process note records that a dependency which
genuinely deletes owned code is a preferred simplification (bar: net
deletion, health, boundary fit, settled seams stay); root AGENTS.md
carries the one-line rule and dsh-find-simplifications now surveys for
hand-rolled-where-a-dependency-exists candidates.

Findings, all bilingual from birth:
- proposed/simplification: eventsource-parser for llm-deepseek SSE,
  node:timers/promises for three hand-rolled sleeps, turndown (or
  minimal 'entities') for tool-web HTML->markdown, gate-script
  consolidation onto mdast/parseArgs/globSync
- proposed/testing: execa + parseArgs + loadEnvFile + vi.waitFor for
  hand-rolled test subprocess plumbing
- proposed/process: pnpm/action-setup for symmetric CI caching
- proposed/feature: evaluate landstrip before building a Windows
  sandbox launcher
- rejected/simplification: ~30 swap verdicts recorded (vscode-jsonrpc,
  p-retry, Ajv, write-file-atomic, msw, hono, better-sqlite3, wireit,
  landstrip-for-linux, YAML consolidation, ...) so the survey is not
  re-litigated from scratch

Also drops the stale prompt/ entry from the AGENTS.md layout map
(workspace instructions live in packages/context/workspace-context).

AGENTS.md

@@ -12,7 +12,6 @@ DeepSeek Harness SDK is a plugin-based agent harness on vendored Cordis: **every
 vendor/      Vendored Cordis source — manifest + sync procedure in vendor/README.md
 packages/    @deepseek-ai/dsh-<pkg> workspaces at packages/<group>/<pkg>/
   core/        product API spine: session, system-prompt, tools, agent, agent-loop
-  prompt/      workspace instructions
   llm/         LLM seam + the DeepSeek adapters (hand-rolled + pi-ai design twin)
   bash/        bash executor seam + local impl + model-facing bash tools
   pty/         persistent PTY seam/backend/tools
@@ -97,6 +96,7 @@ Real-API tests and demos read `DEEPSEEK_API_KEY`, optional `DEEPSEEK_BASE_URL`,
 - **Model-visible ⟺ logged**: anything that reaches a model request must be reconstructable from the session log; a new model-visible input requires a session event.
 - **Plugins, not loop changes**: new behavior goes on the documented extension seams; changing `agent-loop` requires updating docs/architecture.md.
 - **Capability seams are three packages** — interface / implementation / consumer; don't split preemptively.
+- **Prefer maintained dependencies over hand-rolling** when the swap genuinely deletes owned code and tests ([policy](.agents/notes/implemented/process/2026-07-26-dependencies-over-hand-rolling.md)).
 - **Explicit > implicit at package seams**: defaulting is an explicit `resolve(request): Spec` step in the owning implementation, never a hidden `?? default` inside `run()` (the `dsh-bash` request/spec split is the template).
 - **No hardcoded tunables in plugins**: deployment-varying choices are validated `Config` fields changeable from cordis.yml; a `DEFAULT_*` constant or test seam is not configurability. Protocol constants, external specs, and security invariants stay fixed.
 - **Misconfiguration fails loud** at load when self-contained, otherwise at the earliest resolvable point; never silently skip a missing referent.