diff --git a/cmd/migrate_cf_data/main.go b/cmd/migrate_cf_data/main.go
index 1bb7421..e5c59e1 100644
--- a/cmd/migrate_cf_data/main.go
+++ b/cmd/migrate_cf_data/main.go
@@ -195,7 +195,7 @@ func runTradingAuditDump(args []string) error {
 	if err != nil {
 		return err
 	}
-	defer f.Close()
+	defer func() { _ = f.Close() }()
 	enc := json.NewEncoder(f)
 	for _, r := range rows {
 		if err := enc.Encode(r); err != nil {
diff --git a/internal/migration/cloudflare_d1_client.go b/internal/migration/cloudflare_d1_client.go
index 296a5b8..cfdefb4 100644
--- a/internal/migration/cloudflare_d1_client.go
+++ b/internal/migration/cloudflare_d1_client.go
@@ -70,7 +70,7 @@ func (c *CloudflareD1Client) Query(ctx context.Context, sql string, params []any
 	if err != nil {
 		return nil, err
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 	raw, err := io.ReadAll(resp.Body)
 	if err != nil {
 		return nil, err
diff --git a/internal/migration/cloudflare_kv_client.go b/internal/migration/cloudflare_kv_client.go
index e3df20b..fd98d67 100644
--- a/internal/migration/cloudflare_kv_client.go
+++ b/internal/migration/cloudflare_kv_client.go
@@ -119,7 +119,7 @@ func (c *CloudflareKVClient) do(ctx context.Context, method, endpoint string) ([
 	if err != nil {
 		return nil, err
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 	body, err := io.ReadAll(resp.Body)
 	if err != nil {
 		return nil, err
diff --git a/internal/migration/report.go b/internal/migration/report.go
index eb0e578..80b453b 100644
--- a/internal/migration/report.go
+++ b/internal/migration/report.go
@@ -36,22 +36,23 @@ func (r *Report) AddSkippedPolicy(reason string)   { r.SkippedPolicy[reason]++ }
 func (r *Report) AddFailed(prefix string)          { r.Failed[prefix]++ }
 
 // Format writes a human-readable summary. Stable ordering (alphabetical) so
-// rerun diffs stay clean.
+// rerun diffs stay clean. Write errors are ignored — callers pass os.Stdout
+// or *bytes.Buffer, where short writes are not actionable.
 func (r *Report) Format(w io.Writer) {
-	fmt.Fprintln(w, "Migration report")
-	fmt.Fprintln(w, "================")
+	_, _ = fmt.Fprintln(w, "Migration report")
+	_, _ = fmt.Fprintln(w, "================")
 	writeSection(w, "Imported", r.Imported)
 	writeSection(w, "Skipped (already present)", r.SkippedExisting)
 	writeSection(w, "Skipped (policy)", r.SkippedPolicy)
 	writeSection(w, "Failed", r.Failed)
-	fmt.Fprintf(w, "TOTAL imported=%d skipped_existing=%d skipped_policy=%d failed=%d\n",
+	_, _ = fmt.Fprintf(w, "TOTAL imported=%d skipped_existing=%d skipped_policy=%d failed=%d\n",
 		sum(r.Imported), sum(r.SkippedExisting), sum(r.SkippedPolicy), sum(r.Failed))
 }
 
 func writeSection(w io.Writer, label string, m map[string]int) {
-	fmt.Fprintf(w, "\n%s:\n", label)
+	_, _ = fmt.Fprintf(w, "\n%s:\n", label)
 	if len(m) == 0 {
-		fmt.Fprintln(w, "  (none)")
+		_, _ = fmt.Fprintln(w, "  (none)")
 		return
 	}
 	keys := make([]string, 0, len(m))
@@ -60,7 +61,7 @@ func writeSection(w io.Writer, label string, m map[string]int) {
 	}
 	sort.Strings(keys)
 	for _, k := range keys {
-		fmt.Fprintf(w, "  %-30s %d\n", k, m[k])
+		_, _ = fmt.Fprintf(w, "  %-30s %d\n", k, m[k])
 	}
 }
 
diff --git a/plans/reports/debugger-260516-1057-ci-lint-failure.md b/plans/reports/debugger-260516-1057-ci-lint-failure.md
new file mode 100644
index 0000000..8e9813f
--- /dev/null
+++ b/plans/reports/debugger-260516-1057-ci-lint-failure.md
@@ -0,0 +1,65 @@
+# Debug + Fix Report — ci.yml lint failure on commit `1f5f304`
+
+**Date:** 2026-05-16
+**Failed run:** https://github.com/tiennm99/miti99bot/actions/runs/25952128154
+**Workflow:** `.github/workflows/ci.yml` job `go (1.25)` step `golangci-lint`
+**Status:** DONE — fixes verified locally; awaiting CI re-run on next commit.
+
+## Root cause
+
+9 `errcheck` violations introduced by commit `d67517e feat(migration): cf→aws migration toolchain ...` and pushed alongside `39491d1` + my `1f5f304` in the same `git push`. The migration-toolchain commit was the first one to add these unchecked errors; prior commit `75e9360` (docs-only) didn't include them. My deploy-workflow commit `1f5f304` is the first that triggered a CI run after `d67517e` landed, so the lint failure surfaced here even though my change touched zero Go files.
+
+**Not** a regression caused by the auto-register workflow change.
+
+## Violations
+
+| File | Line | Pattern |
+|---|---|---|
+| `cmd/migrate_cf_data/main.go` | 198 | `defer f.Close()` |
+| `internal/migration/cloudflare_d1_client.go` | 73 | `defer resp.Body.Close()` |
+| `internal/migration/cloudflare_kv_client.go` | 122 | `defer resp.Body.Close()` |
+| `internal/migration/report.go` | 41,42,47,52,54,63 | `fmt.Fprintln` / `fmt.Fprintf` to `io.Writer` |
+
+## Fixes applied
+
+**Close calls** — wrap in anonymous defer with underscore-assignment, matching the established project pattern in `internal/modules/lolschedule/api_client.go:162` and `internal/modules/trading/prices.go:90`:
+
+```go
+defer func() { _ = resp.Body.Close() }()
+```
+
+**Fprint* calls** — explicit underscore-assignment, idiomatic for best-effort writes to `os.Stdout` / `*bytes.Buffer` (the only callers per `grep .Format(`):
+
+```go
+_, _ = fmt.Fprintln(w, "Migration report")
+```
+
+Also added one comment to `Report.Format` noting the rationale (write errors not actionable for the actual callers).
+
+## Verification
+
+| Check | Result |
+|---|---|
+| `go vet ./...` | clean |
+| `golangci-lint run ./...` | `0 issues.` |
+| `go test -race -count=1 ./...` | all 18 packages pass (incl. `internal/migration`) |
+| `go build ./...` | clean |
+
+## Files changed (4 production)
+
+- `cmd/migrate_cf_data/main.go`
+- `internal/migration/cloudflare_d1_client.go`
+- `internal/migration/cloudflare_kv_client.go`
+- `internal/migration/report.go`
+
+## Why not just add `//nolint:errcheck`?
+
+Project has zero `//nolint` directives in `internal/` or `cmd/` (verified by `grep -rn "nolint"` — no hits). Anonymous-defer + `_, _ =` matches the existing house style, so no new lint-suppression convention.
+
+## Why not change `Report.Format` to return `error`?
+
+API change for ~6 lines of cosmetic improvement; only 1 production caller (`cmd/migrate_cf_data/main.go:172 — report.Format(os.Stdout)`) which would discard the error anyway since stdout writes are not recoverable. KISS / YAGNI.
+
+## Unresolved questions
+
+None.