diff --git a/CHANGELOG.md b/CHANGELOG.md
index f69fe9d..8a8b439 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,16 @@ Release history for the `opsmill` spec-kit extension (`extension.yml`).
 The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this artifact adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Changed
+- `speckit.opsmill.prep` Phase 2 (Plan) gains a research directive for
+  constrained third-party dependencies: when a dependency lacks a capability
+  the feature needs, the research phase must evaluate the dependency's
+  extension mechanism and upstream contribution before designing a
+  workaround, and record the decision in `research.md`. Applies to
+  `speckit.opsmill.auto` as well via its delegation to prep.
+
 ## [1.1.0] - 2026-06-19
 
 ### Added
diff --git a/commands/prep.md b/commands/prep.md
index 2eb5816..159695e 100644
--- a/commands/prep.md
+++ b/commands/prep.md
@@ -35,6 +35,11 @@ Invoke the `speckit-specify` skill with the user's feature description (`$ARGUME
 Invoke the `speckit-plan` skill.
 
 - Complete the full plan workflow: research unknowns, generate `plan.md`, `research.md`, `data-model.md`, API contracts, `quickstart.md`.
+- **Research directive — constrained third-party dependencies.** If the feature depends on a third-party library or tool that does not support something the implementation needs, you MUST evaluate extending that dependency before designing around the gap:
+  - Check for a built-in extension mechanism (plugin system, hooks, middleware, custom providers, etc.) that could supply the missing capability.
+  - Consider an upstream contribution (patch, feature PR) when no extension mechanism fits.
+  - Record the evaluation in `research.md` as an explicit decision: the chosen approach, the rationale, and the extension/upstream alternatives that were rejected and why.
+  - Only fall back to working around the limitation in our own codebase when both routes are infeasible (e.g., unmaintained upstream, unacceptable timeline) — and record why. The point is to avoid overly complex implementations whose only cause is a dependency gap that the dependency itself was designed to let you fill.
 - Make all design decisions autonomously.
 - Commit the plan artifacts.