From ab723a73a628289e75bae708ef83146899f3e620 Mon Sep 17 00:00:00 2001
From: scanner <280983584+hivecommons-hive[bot]@users.noreply.github.com>
Date: Sun, 18 Oct 2026 13:34:41 -0400
Subject: [PATCH] fix: apply PLUK_LOG_MAX_BYTES cap even when log has fewer
 than keepLines lines

Signed-off-by: scanner <280983584+hivecommons-hive[bot]@users.noreply.github.com>
---
 changelog.d/fixed-283.md       |  1 +
 src/run-dir.ts                 |  2 +-
 test/default-fallbacks.test.js |  9 ++++-----
 test/run-dir.test.js           | 15 +++++++++++++++
 4 files changed, 21 insertions(+), 6 deletions(-)
 create mode 100644 changelog.d/fixed-283.md

diff --git a/changelog.d/fixed-283.md b/changelog.d/fixed-283.md
new file mode 100644
index 0000000..44186a2
--- /dev/null
+++ b/changelog.d/fixed-283.md
@@ -0,0 +1 @@
+- Log rotation now applies the `PLUK_LOG_MAX_BYTES` cap even when the log has fewer than `PLUK_LOG_KEEP_LINES` lines (#283).
diff --git a/src/run-dir.ts b/src/run-dir.ts
index 2ebc453..83d8912 100644
--- a/src/run-dir.ts
+++ b/src/run-dir.ts
@@ -175,7 +175,6 @@ export function rotateLogFileIfNeeded(
   const lines = snapshot.toString('utf-8').split('\n');
   const hasTrailingNewline = lines.length > 0 && lines[lines.length - 1] === '';
   const usableLines = hasTrailingNewline ? lines.slice(0, -1) : lines;
-  if (usableLines.length <= keepLines) return false;
 
   // A snapshot ending mid-line keeps that partial line unterminated so the
   // rest of it, copied from past the snapshot below, completes it.
@@ -188,6 +187,7 @@ export function rotateLogFileIfNeeded(
     keptBytes -= Buffer.byteLength(kept[drop]!, 'utf-8') + 1;
     drop++;
   }
+  if (drop === 0 && kept.length === usableLines.length) return false;
   kept = kept.slice(drop);
   const rebuilt = Buffer.from(kept.join('\n') + (hasTrailingNewline ? '\n' : ''), 'utf-8');
 
diff --git a/test/default-fallbacks.test.js b/test/default-fallbacks.test.js
index f1f070e..65d39b9 100644
--- a/test/default-fallbacks.test.js
+++ b/test/default-fallbacks.test.js
@@ -94,17 +94,16 @@ test('defaultRunDir falls back to pluk-user when process.getuid is unavailable',
 
 // --- rotateLogFileIfNeeded with too few lines to trim -----------------------------
 
-test('rotateLogFileIfNeeded leaves an oversized log alone when it has no more than keepLines lines', () => {
+test('rotateLogFileIfNeeded trims an oversized log with fewer than keepLines lines to the byte cap', () => {
   const base = mkdtempSync(join(tmpdir(), 'pluk-fallbacks-'));
   try {
     const file = join(base, 'wide.jsonl');
-    // Two lines, each far past maxBytes: over the byte threshold, but
-    // trimming to the last 5 lines would keep everything, so no rewrite.
+    // Two lines, each far past maxBytes: only the newest line is kept.
     const content = `{"pad":"${'x'.repeat(200)}"}\n{"pad":"${'y'.repeat(200)}"}\n`;
     writeFileSync(file, content);
 
-    assert.strictEqual(rotateLogFileIfNeeded(file, { maxBytes: 10, keepLines: 5 }), false);
-    assert.equal(readFileSync(file, 'utf-8'), content);
+    assert.strictEqual(rotateLogFileIfNeeded(file, { maxBytes: 10, keepLines: 5 }), true);
+    assert.equal(readFileSync(file, 'utf-8'), `{"pad":"${'y'.repeat(200)}"}\n`);
   } finally {
     rmSync(base, { recursive: true, force: true });
   }
diff --git a/test/run-dir.test.js b/test/run-dir.test.js
index d5747b8..10e50cb 100644
--- a/test/run-dir.test.js
+++ b/test/run-dir.test.js
@@ -249,6 +249,21 @@ test('rotateLogFileIfNeeded trims an oversized log to the last N lines', () => {
   }
 });
 
+test('rotateLogFileIfNeeded applies the byte cap when the log has fewer than keepLines lines', () => {
+  const base = tempBase();
+  try {
+    const file = join(base, 'few.jsonl');
+    const lines = Array.from({ length: 6 }, (_, i) => `{"n":${i}}`);
+    writeFileSync(file, lines.join('\n') + '\n');
+
+    // Each line is 8 bytes with its newline; 20 bytes fits the last two.
+    assert.strictEqual(rotateLogFileIfNeeded(file, { maxBytes: 20, keepLines: 100 }), true);
+    assert.equal(readFileSync(file, 'utf-8'), lines.slice(-2).join('\n') + '\n');
+  } finally {
+    rmSync(base, { recursive: true, force: true });
+  }
+});
+
 test('rotateLogFileIfNeeded is a no-op for a missing file', () => {
   const base = tempBase();
   try {