fix(completion): gate block headers behind a blank line

The popup offered [[feature]]/[[milestone]] on every fresh line — right
under the last property or straight after a header. Only volunteer them
once there's a blank line above (the "two new lines" convention); typing
a bare `[` still summons them anywhere. Property keys are unchanged.

src/components/completion.test.ts

@@ -14,11 +14,12 @@ function labelsAt(marked: string): string[] {
 }
 
 describe("completion context", () => {
-  it("offers plan keys and block headers on an empty top-level line", () => {
-    expect(labelsAt("|")).toEqual(["title", "start", "end", "[[feature]]", "[[milestone]]"])
+  it("offers plan keys on an empty top-level line", () => {
+    // Headers wait for a blank line above; at the very top there's nothing above.
+    expect(labelsAt("|")).toEqual(["title", "start", "end"])
   })
 
-  it("offers feature keys inside a [[feature]] block", () => {
+  it("offers feature keys inside a [[feature]] block, no headers on the first line", () => {
     expect(labelsAt("[[feature]]\n|")).toEqual([
       "name",
       "start",
@@ -28,14 +29,27 @@ describe("completion context", () => {
       "status",
       "learning",
       "note",
-      "[[feature]]",
-      "[[milestone]]",
     ])
   })
 
-  it("offers milestone keys inside a [[milestone]] block", () => {
-    expect(labelsAt("[[milestone]]\n|")).toEqual([
-      "name",
+  it("offers milestone keys inside a [[milestone]] block, no headers on the first line", () => {
+    expect(labelsAt("[[milestone]]\n|")).toEqual(["name", "week", "requires"])
+  })
+
+  it("keeps offering remaining keys on a single new line, still without headers", () => {
+    expect(labelsAt('[[milestone]]\nname = "M"\n|')).toEqual(["week", "requires"])
+  })
+
+  it("volunteers block headers only after a blank line (two new lines)", () => {
+    const filled = '[[milestone]]\nname = "M"\nweek = 2026-01-01\nrequires = []'
+    // Directly under the last property: nothing left to add ⇒ no popup.
+    expect(getCompletions(...atCaret(`${filled}\n|`))).toBeNull()
+    // A blank line signals a new block is wanted ⇒ offer the headers.
+    expect(labelsAt(`${filled}\n\n|`)).toEqual(["[[feature]]", "[[milestone]]"])
+  })
+
+  it("volunteers headers after a blank line even with keys still open", () => {
+    expect(labelsAt('[[milestone]]\nname = "M"\n\n|')).toEqual([
       "week",
       "requires",
       "[[feature]]",

src/components/completion.ts

@@ -108,7 +108,16 @@ export function getCompletions(
     const keys =
       block === "feature" ? FEATURE_KEYS : block === "milestone" ? MILESTONE_KEYS : PLAN_KEYS
     const taken = presentKeys(source, lineStart, block)
-    const items = filter([...keys.filter((k) => !taken.has(k.label)), ...HEADERS], word)
+    const remaining = keys.filter((k) => !taken.has(k.label))
+    // Volunteer a new block header only once there's a blank line above: a new
+    // [[…]] wants a gap before it, so offering one right under the last property
+    // (or straight after the header line) pops the menu up too eagerly. Typing a
+    // bare `[` still summons headers anywhere (handled above). With all keys set
+    // and no gap, `remaining` is empty ⇒ result() returns null ⇒ no popup.
+    const items = filter(
+      blankLineAbove(source, lineStart) ? [...remaining, ...HEADERS] : remaining,
+      word,
+    )
     return result(caret - word.length, caret, items)
   }
 
@@ -119,6 +128,14 @@ function result(from: number, to: number, items: Completion[]): CompletionContex
   return items.length ? { from, to, items } : null
 }
 
+/** Is the line directly above the caret's line blank (empty or whitespace only)?
+ *  Gates header suggestions to the "two new lines" rule — see the key branch. */
+function blankLineAbove(source: string, lineStart: number): boolean {
+  if (lineStart === 0) return false // top of the document — nothing above
+  const prevStart = source.lastIndexOf("\n", lineStart - 2) + 1
+  return /^[ \t]*$/.test(source.slice(prevStart, lineStart - 1))
+}
+
 /** Today as yyyy-mm-dd in the author's local zone — the calendar day they see,
  *  not UTC's (which slips a day near midnight). Injectable keeps tests stable. */
 function todayYmd(): string {