diff --git a/src/resources/extensions/gsd/prompts/complete-milestone.md b/src/resources/extensions/gsd/prompts/complete-milestone.md
index 9646d236a..0018fe787 100644
--- a/src/resources/extensions/gsd/prompts/complete-milestone.md
+++ b/src/resources/extensions/gsd/prompts/complete-milestone.md
@@ -23,7 +23,8 @@ Then:
 6. Write `{{milestoneSummaryPath}}` using the milestone-summary template. Fill all frontmatter fields and narrative sections. The `requirement_outcomes` field must list every requirement that changed status with `from_status`, `to_status`, and `proof`.
 7. Update `.gsd/REQUIREMENTS.md` if any requirement status transitions were validated in step 5.
 8. Update `.gsd/PROJECT.md` to reflect milestone completion and current project state.
-9. Do not commit manually — the system auto-commits your changes after this unit completes.
+9. Review all slice summaries for cross-cutting lessons, patterns, or gotchas that emerged during this milestone. Append any non-obvious, reusable insights to `.gsd/KNOWLEDGE.md`.
+10. Do not commit manually — the system auto-commits your changes after this unit completes.
 
 **Important:** Do NOT skip the success criteria and definition of done verification (steps 3-4). The milestone summary must reflect actual verified outcomes, not assumed success. If any criterion was not met, document it clearly in the summary and do not mark the milestone as passing verification.
 
diff --git a/src/resources/extensions/gsd/prompts/complete-slice.md b/src/resources/extensions/gsd/prompts/complete-slice.md
index e9490a924..72c51e947 100644
--- a/src/resources/extensions/gsd/prompts/complete-slice.md
+++ b/src/resources/extensions/gsd/prompts/complete-slice.md
@@ -27,9 +27,10 @@ Then:
 6. Write `{{sliceSummaryPath}}` (compress all task summaries).
 7. Write `{{sliceUatPath}}` — a concrete UAT script with real test cases derived from the slice plan and task summaries. Include preconditions, numbered steps with expected outcomes, and edge cases. This must NOT be a placeholder or generic template — tailor every test case to what this slice actually built.
 8. Review task summaries for `key_decisions`. Append any significant decisions to `.gsd/DECISIONS.md` if missing.
-9. Mark {{sliceId}} done in `{{roadmapPath}}` (change `[ ]` to `[x]`)
-10. Do not run git commands — the system commits your changes and handles any merge after this unit succeeds.
-11. Update `.gsd/PROJECT.md` if it exists — refresh current state if needed.
+9. Review task summaries for patterns, gotchas, or non-obvious lessons learned. If any would save future agents from repeating investigation or hitting the same issues, append them to `.gsd/KNOWLEDGE.md`. Only add entries that are genuinely useful — don't pad with obvious observations.
+10. Mark {{sliceId}} done in `{{roadmapPath}}` (change `[ ]` to `[x]`)
+11. Do not run git commands — the system commits your changes and handles any merge after this unit succeeds.
+12. Update `.gsd/PROJECT.md` if it exists — refresh current state if needed.
 
 **You MUST do ALL THREE before finishing: (1) write `{{sliceSummaryPath}}`, (2) write `{{sliceUatPath}}`, (3) mark {{sliceId}} as `[x]` in `{{roadmapPath}}`. The unit will not be marked complete if any of these files are missing.**