test(#1074): agent-size-budget per-file baseline + line→byte rebase (PR 3/3) (#1097)

Extends the #1074 scheme to tests/agent-size-budget.test.cjs, which used the
same assertTightCeiling tier ratchet but was still line-based (never rebased in
#717). Completes the migration — the last part of the #1074 epic.

- Rebase agent sizing from lines to LF-normalized bytes (#717/#683).
- Delete the 'SIZE: tier anti-creep' describe (3 assertTightCeiling tests);
  add a per-agent baseline (tests/agent-size-baseline.json) as the primary
  anti-creep, and byte hard caps (XL 56 KiB / LARGE 48 KiB / DEFAULT 24 KiB),
  each above its tier high-water with real headroom. No separate new-file cap:
  a net-new agent is DEFAULT-tier, already bounded by the DEFAULT cap.
- Keep the agent-classification tests verbatim.
- scripts/workflow-size.cjs: add generic measureMdFiles(dir, predicate)
  (workflows + agents share one byte-measurement path); measureWorkflows now
  delegates to it.
- scripts/update-size-baseline.cjs: one 'npm run size:baseline' now regenerates
  BOTH the workflow and agent baselines (gsd-* filter for agents).

Rebased onto next after PR 2/3 (#1096) merged: replicate the
scripts/lib/workflow-size.cjs -> scripts/workflow-size.cjs move (PR 1/3) across
the generator and the agent test's require; regenerate the agent baseline
against current agents (a uniform +170 B preamble drift on all 33 since
authoring).

Addresses the #1097 review (trek-e):
- BLOCKER (acceptance criterion 5): document the agent contract in CONTEXT.md.
  Adds RULESET.AGENT_SIZE_BUDGET (caps 57344/49152/24576, per-agent baseline,
  dual size:baseline, shared measureMdFiles seam) and disambiguates it from the
  separate DEFECT.AGENT-FILE-SIZE-CAP-BREACH 45K-CHAR guard (two units, two
  purposes).
- Docs: now that #1096's docs/TESTING-SUITES.md "Workflow size budget" section
  is in next, fold in the agent coverage here (renamed to "Workflow & agent
  size budget"): agent caps + per-agent baseline + the how-to + reference rows,
  and the disambiguation from the 45K-char guard.
- Minor (negative proof): add a boundary-fixture test exercising the hard-cap
  comparison at cap-1/cap/cap+1 through the real lfByteCount path, so a future
  threshold/operator edit can't silently neuter a cap.
- Nit: align the tier test name wording ("stays within") with the <= operator.

Negative proof on a real tracked agent (gsd-planner): baseline catches +10 B;
XL hard cap catches 57,516 > 57,344 with the baseline current.

Closes #1095 (PR 3/3 child); landing this completes the #1074 epic.

scripts/workflow-size.cjs

@@ -51,18 +51,40 @@ function listWorkflowStems(dir = WORKFLOWS_DIR) {
 }
 
 /**
- * Measure every top-level workflow file, keyed by filename (`<stem>.md`).
+ * Measure every top-level `.md` file in `dir`, keyed by filename, byte sizes.
+ * Generic over directory and an optional filename predicate — used for both
+ * workflows (`gsd-core/workflows/*.md`) and agents (`agents/gsd-*.md`) so the
+ * size guards and the baseline generator share one measurement path (#1074).
+ * Non-recursive by design.
  *
- * @param {string} [dir] - Workflows directory (defaults to the canonical one).
- * @returns {Object<string, number>} Map of `<stem>.md` → LF byte size, with
- *   keys inserted in sorted order.
+ * @param {string} dir - Directory to scan.
+ * @param {function(string): boolean} [predicate] - Filename filter (default: all `.md`).
+ * @returns {Object<string, number>} Map of filename → LF byte size, keys sorted.
  */
-function measureWorkflows(dir = WORKFLOWS_DIR) {
+function measureMdFiles(dir, predicate = () => true) {
   const out = {};
-  for (const stem of listWorkflowStems(dir)) {
-    out[`${stem}.md`] = lfByteCount(path.join(dir, `${stem}.md`));
-  }
+  const names = fs
+    .readdirSync(dir)
+    .filter((f) => f.endsWith('.md') && predicate(f))
+    .sort();
+  for (const name of names) out[name] = lfByteCount(path.join(dir, name));
   return out;
 }
 
-module.exports = { WORKFLOWS_DIR, lfByteCount, listWorkflowStems, measureWorkflows };
+/**
+ * Measure every top-level workflow file, keyed by filename (`<stem>.md`).
+ *
+ * @param {string} [dir] - Workflows directory (defaults to the canonical one).
+ * @returns {Object<string, number>} Map of `<stem>.md` → LF byte size, sorted.
+ */
+function measureWorkflows(dir = WORKFLOWS_DIR) {
+  return measureMdFiles(dir);
+}
+
+module.exports = {
+  WORKFLOWS_DIR,
+  lfByteCount,
+  listWorkflowStems,
+  measureMdFiles,
+  measureWorkflows,
+};