diff --git a/lib/__tests__/core.test.ts b/lib/__tests__/core.test.ts
index 40a9b85..a7b0674 100644
--- a/lib/__tests__/core.test.ts
+++ b/lib/__tests__/core.test.ts
@@ -115,3 +115,103 @@ test("unknown alias exits 1 with empty stdout", async () => {
   expect(r.code).toBe(1);
   expect(r.stdout.trim()).toBe("");
 });
+
+// ─────────────────────────────────────────────────────────────────────────
+// W6.5 — SIGPIPE immunity under bin/subctl's `set -uo pipefail`
+// ─────────────────────────────────────────────────────────────────────────
+//
+// Regression for the 2026-06-11 resolver failure: subctl_list_accounts is
+// slow (5 _subctl_trim command substitutions per row), and piping it
+// straight into an early-exit awk closed the pipe mid-write. The producer
+// took SIGPIPE, pipefail turned the pipeline status into 141, and
+// `resolved=$(subctl_resolve_alias …) || subctl_die "unknown account"`
+// died even though the alias had already been printed and captured.
+// Position-dependent: an alias EARLY in a long accounts.conf always lost
+// the race (reproduced 5/5 on the pre-fix code with this exact fixture),
+// while last-row aliases always won. These tests run the helpers under
+// the same shell options bin/subctl sets, with the target on row 1 of a
+// 50-row roster so the race is deterministic, and repeat each lookup to
+// catch flaky scheduling.
+
+function setupWideRoster(): Fixture {
+  const root = mkdtempSync(join(tmpdir(), "subctl-core-sigpipe-"));
+  const configDir = join(root, "userconfig");
+  mkdirSync(configDir, { recursive: true });
+  const accountsConf = join(configDir, "accounts.conf");
+  const rows = [
+    "# 50-row roster — target EARLY so an early-exit awk races the producer",
+    "openai-jason    | openai-codex | oj@example.com    | ~/.codex-jason     | the row that lost the race",
+  ];
+  for (let i = 1; i <= 49; i++) {
+    rows.push(
+      `claude-filler${i}  | claude       | f${i}@example.com   | ~/.claude-f${i}      | filler row ${i}`,
+    );
+  }
+  writeFileSync(accountsConf, rows.join("\n") + "\n");
+  return { root, accountsConf };
+}
+
+/** Run a core.sh snippet under bin/subctl's exact shell options. */
+async function runUnderPipefail(d: Fixture, snippet: string): Promise<BashResult> {
+  const proc = Bun.spawn(
+    ["bash", "-c", `set -uo pipefail; source "${CORE_SH}"; ${snippet}`],
+    {
+      env: {
+        ...process.env,
+        SUBCTL_REPO_ROOT: REPO_ROOT,
+        SUBCTL_CONFIG_DIR: join(d.root, "userconfig"),
+        SUBCTL_ACCOUNTS_CONF: d.accountsConf,
+        NO_COLOR: "1",
+      },
+      stdout: "pipe",
+      stderr: "pipe",
+    },
+  );
+  const code = await proc.exited;
+  const stdout = await new Response(proc.stdout).text();
+  const stderr = await new Response(proc.stderr).text();
+  return { code, stdout, stderr };
+}
+
+test("pipefail: early-row alias resolves with exit 0, every time (5/5)", async () => {
+  d = setupWideRoster();
+  for (let run = 1; run <= 5; run++) {
+    const r = await runUnderPipefail(d, `subctl_resolve_alias openai-jason`);
+    expect(r.code).toBe(0);
+    expect(r.stdout.trim()).toBe("openai-jason");
+  }
+});
+
+test("pipefail: early-row field lookup returns the field with exit 0 (5/5)", async () => {
+  d = setupWideRoster();
+  for (let run = 1; run <= 5; run++) {
+    const r = await runUnderPipefail(d, `subctl_account_field openai-jason 2`);
+    expect(r.code).toBe(0);
+    expect(r.stdout.trim()).toBe("openai-codex");
+  }
+});
+
+test("pipefail: the bin/subctl caller shape (capture || die) survives", async () => {
+  d = setupWideRoster();
+  // The exact consumption pattern that produced "unknown account": a
+  // command substitution followed by `|| die`.
+  const r = await runUnderPipefail(
+    d,
+    `resolved=$(subctl_resolve_alias openai-jason) || subctl_die "unknown account: openai-jason"; printf '%s\\n' "$resolved"`,
+  );
+  expect(r.code).toBe(0);
+  expect(r.stdout.trim()).toBe("openai-jason");
+  expect(r.stderr).not.toContain("unknown account");
+});
+
+test("pipefail: bare→prefixed and prefixed→bare passes stay intact on the wide roster", async () => {
+  d = setupWideRoster();
+  // Bare → prefixed: filler1 → claude-filler1 (pass 2).
+  const bare = await runUnderPipefail(d, `subctl_resolve_alias filler1`);
+  expect(bare.code).toBe(0);
+  expect(bare.stdout.trim()).toBe("claude-filler1");
+  // No match still exits 1 with empty stdout (pass 3 falls through).
+  const miss = await runUnderPipefail(d, `subctl_resolve_alias nope-never`);
+  expect(miss.code).toBe(1);
+  expect(miss.stdout.trim()).toBe("");
+});
diff --git a/lib/core.sh b/lib/core.sh
index d5bbe2e..b704a90 100755
--- a/lib/core.sh
+++ b/lib/core.sh
@@ -77,11 +77,22 @@ subctl_list_accounts() {
   done < "$SUBCTL_ACCOUNTS_CONF"
 }
 
+# SIGPIPE note (W6.5): never pipe subctl_list_accounts straight into an
+# early-exit awk (`{print; exit}`). The producer is slow (5 _subctl_trim
+# command substitutions per row); awk's early exit closes the pipe while
+# the producer is mid-write, the producer takes SIGPIPE, and under
+# bin/subctl's `set -uo pipefail` the pipeline status becomes 141 — so the
+# lookup "fails" even though the answer was already printed and captured.
+# Position-dependent: aliases early in accounts.conf always lost the race
+# (reproduced 5/5 with openai-jason mid-file, 2026-06-11). Buffer the
+# roster once and feed awk via herestring instead.
+
 # Get a specific field for an alias. Field index: 1=alias 2=provider 3=email 4=config_dir 5=description
 # Usage: subctl_account_field <alias> <field_num>
 subctl_account_field() {
-  local want="$1" idx="$2"
-  subctl_list_accounts | awk -F'\t' -v w="$want" -v i="$idx" '$1==w {print $i; exit}'
+  local want="$1" idx="$2" all
+  all=$(subctl_list_accounts)
+  awk -F'\t' -v w="$want" -v i="$idx" '$1==w {print $i; exit}' <<<"$all"
 }
 
 # Resolve an alias that may be given with or without the provider prefix.
@@ -90,20 +101,21 @@ subctl_account_field() {
 # profiles often carry bare aliases while muscle memory types prefixed ones).
 # Returns the canonical alias on stdout, or exit 1 if no match.
 subctl_resolve_alias() {
-  local want="$1" hit
-  subctl_list_accounts | awk -F'\t' -v w="$want" '
+  local want="$1" hit all
+  all=$(subctl_list_accounts)
+  awk -F'\t' -v w="$want" '
     $1==w { print $1; found=1; exit }
     END { if (!found) exit 1 }
-  ' && return 0
+  ' <<<"$all" && return 0
   # Bare → prefixed: any alias ending in "-$want"
-  hit=$(subctl_list_accounts | awk -F'\t' -v w="$want" '
+  hit=$(awk -F'\t' -v w="$want" '
     $1 ~ "-" w "$" { print $1; exit }
-  ')
+  ' <<<"$all")
   [[ -n "$hit" ]] && { printf '%s\n' "$hit"; return 0; }
   # Prefixed → bare: "$want" is exactly "<provider>-<alias>"
-  hit=$(subctl_list_accounts | awk -F'\t' -v w="$want" '
+  hit=$(awk -F'\t' -v w="$want" '
     w == $2 "-" $1 { print $1; exit }
-  ')
+  ' <<<"$all")
   [[ -n "$hit" ]] && { printf '%s\n' "$hit"; return 0; }
   # No match: fail so callers die with "unknown account: <name>" instead of
   # threading an empty alias into downstream field lookups.