feat(#192): add evidence cap to retro-analysis skill

internal/scaffold/fullsend-repo/skills/retro-analysis/SKILL.md

@@ -123,6 +123,62 @@ Use multiple searches with different keyword combinations if the first returns n
 
 When skipping, note the duplicate in your `summary` field so the human understands what was filtered and why.
 
+**Evidence cap for tracked patterns**
+
+This check runs after the general duplicate check above and applies an
+additional cap specifically to evidence-type proposals that survive
+duplicate filtering.
+
+When a candidate proposal provides additional evidence for a parent issue
+that is already tracked (i.e., the proposal would be filed as
+"Evidence for #N: ..." referencing an existing open issue), check how many
+open evidence issues already exist for that parent before proposing.
+
+Evidence proposals **must** use the title prefix `Evidence for #N: `
+(where N is the parent issue number). This convention is required so the
+count query below can reliably identify evidence issues.
+
+Dispatch a subagent to query the count:
+
+> "Count the open issues in `<target_repo>` whose title starts with
+> 'Evidence for #N:' where N is `<parent_number>`. Return the count."
+
+The subagent should run:
+
+```bash
+gh api \
+  "search/issues?q=repo:<target_repo>+is:issue+is:open+in:title+\"Evidence+for+%23<parent_number>:\"" \
+  --jq '.total_count'
+```
+
+Note: the query uses `in:title` and includes the trailing colon to
+reduce false positives from unrelated issues that mention "Evidence
+for #N" in passing.
+
+If the count query fails or returns an error (e.g., rate limiting,
+network error, auth failure), **fail open** — proceed with the proposal
+as if the cap were not reached. Note the query failure in the `summary`
+field so the human is aware the cap could not be evaluated.
+
+**If the count is >= 5, skip the evidence proposal entirely.** The
+pattern is already well-documented — additional evidence provides
+diminishing returns and creates tracking overhead without adding new
+information.
+
+Instead of filing the proposal:
+
+1. Do not include it in the `proposals` array.
+2. In the `summary` field, note that the pattern is already
+   well-documented. Mention the parent issue number and the current
+   PR or issue as an additional data point. For example: "Pattern
+   tracked by #N already has sufficient evidence (M open data-point
+   issues). This PR/issue provides another data point but no new
+   issue was filed."
+
+This cap applies only to evidence issues for already-tracked parent
+issues. Proposals for genuinely new patterns or distinct improvements
+are not subject to this limit.
+
 ## Localization guidance
 
 When deciding where a proposed change belongs: