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/skills/dsh-find-simplifications/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: dsh-find-simplifications
-description: 'Use when working in the deepseek-harness repo to find non-obvious simplification candidates, write proposed Agent Notes or inline TODO/FIXME/XXX notes, audit or coalesce superseded Agent Notes, or fold worthwhile simplification ideas from another PR; especially for dead, duplicated, speculative, over-built, or added-then-removed surfaces.'
+description: 'Use when working in the deepseek-harness repo to find non-obvious simplification candidates, write proposed Agent Notes or inline TODO/FIXME/XXX notes, audit or coalesce superseded Agent Notes, or fold worthwhile simplification ideas from another PR; especially for dead, duplicated, speculative, over-built, added-then-removed, or hand-rolled-where-a-dependency-exists surfaces.'
 ---
 
 # Finding DeepSeek Harness Simplifications
@@ -25,6 +25,7 @@ A strong simplification removes, folds, or demotes something real and has clear
 - A package boundary exists only for test/demo/support code and adds publish or dependency overhead.
 - A feature implements speculative product generality: multi-session/session-load, background task rosters, live registry invalidation, mid-turn steering, tool-owned UI rendering, and similar shapes with no product owner.
 - An invariant, rollback path, set of expected outputs, or special-case test exists only to protect an unused surface.
+- Hand-rolled code reimplements what a well-maintained external package or a Node builtin at the engine floor already provides, and the swap would delete the implementation plus its dedicated tests ([dependency policy](../../notes/implemented/process/2026-07-26-dependencies-over-hand-rolling.md)).
 - The simplified behavior may differ slightly, but the new behavior is still reasonable and easier to explain.
 
 Thin candidates are usually not enough for an Agent Note: deleting one typo, running `knip` once, removing an intentionally documented backend/adapter, or flagging "this looks complex" without call-site proof.
@@ -49,6 +50,17 @@ Classify every defensive copy, freeze, validator, and callback capture by the bo
 
 For complex asynchronous code, draw the ownership graph and map each sentinel, readiness promise, cancellation path, disposer, and state flag to a distinct owner or transition. When several mechanisms mirror the same liveness or settlement fact, propose one transaction or lifecycle controller instead. Preserve separate machinery where it protects a real boundary: synchronous publication and rollback, callback containment, first-terminal-outcome arbitration, worker/process ownership, or dispose-to-quiescence.
 
+## Hand-Rolled Code Versus A Dependency
+
+Introducing a dependency is a valid simplification move, not a policy exception: the [dependency policy](../../notes/implemented/process/2026-07-26-dependencies-over-hand-rolling.md) owns the bar. When surveying, ask of protocol parsers, framers, retry/backoff loops, glob matchers, diff engines, and similar infrastructure: does a well-maintained npm package or a Node builtin at the repo's engine floor already do this?
+
+Prove a dependency-swap candidate like any other, plus:
+
+- Read the hand-rolled implementation and name the exact surface the package covers; residual semantics the package does not cover count against the swap and stay in the Agent Note.
+- Check the package's health honestly (maintenance, adoption, transitive footprint) and prefer builtins when the engine floor has them.
+- Check the Agent Note tree first: schemastery, vendored Cordis, the twin adapters, and other recorded seams are settled — a swap that collapses one needs to beat the recorded rationale, not just cite the policy.
+- Weigh net deletion: implementation plus dedicated tests plus docs, minus the glue that remains. A wrapper that relocates the same complexity is not a win.
+
 ## Prove Or Reject Each Candidate
 
 For every symbol or behavior, classify consumers before writing: