fix(teams): a private answer has to be private, and the deferral decides that

Found on the live rig. Ephemerality is a property of the DEFERRAL, which happens
before the handler has said anything — so the envelope's `ephemeral` was being
read and then ignored, and `/guild`'s "not shown to your account" refusal was
posted into the channel, announcing a member's access level to everyone in it.

When the handler wants privacy the deferral did not give it, the deferred reply
is now withdrawn and the answer arrives as an ephemeral follow-up. The
interaction token stays valid, so this is a supported path and not a trick; the
cost is a "thinking..." that appears and vanishes. There is no reverse case — a
command deferred privately must not become public because a handler omitted a
flag — and a refusal is always private whatever the command's usual privacy.

Co-Authored-By: Claude <noreply@anthropic.com>

bot/test/dynamicCommands.test.js

@@ -53,6 +53,7 @@ function fakeInteraction({ commandName = 'guild', options = {}, userId = '555' }
     },
     deferReply: async (payload) => calls.push(['defer', payload]),
     editReply: async (payload) => calls.push(['edit', payload]),
+    deleteReply: async () => calls.push(['delete']),
     followUp: async (payload) => calls.push(['followUp', payload]),
   }
 }
@@ -195,6 +196,46 @@ test('a notice is not repeated when the answer was already private', async () =>
 
 // Every failure path EDITS. Replying to a deferred interaction throws, so a
 // refusal that used reply() would turn a clean "no" into an unhandled error.
+// Ephemerality is fixed at the DEFERRAL, which happens before the handler has
+// said anything — so honouring a per-answer flag needs the deferred reply
+// withdrawn. The live walk caught the version that ignored it posting "guild
+// information is not shown to your account" into the channel, which announces a
+// member's access level to everyone in it.
+test('a handler asking for privacy gets it, even though the deferral was public', async () => {
+  answers([definition()])
+  await dynamic.pull()
+  appInternal.dispatchCommand = async () => ({
+    ok: true, data: { ok: true, response: { text: 'just for you', ephemeral: true } },
+  })
+  const interaction = fakeInteraction()
+  await dynamic.execute(interaction)
+  assert.deepEqual(interaction.calls.map(([kind]) => kind), ['defer', 'delete', 'followUp'])
+  assert.deepEqual(interaction.calls.at(-1)[1], { content: 'just for you', ephemeral: true })
+})
+
+test('an already-private deferral just edits — no second message', async () => {
+  answers([definition({ access: 'linked' })])
+  await dynamic.pull()
+  appInternal.dispatchCommand = async () => ({
+    ok: true, data: { ok: true, response: { text: 'private', ephemeral: true } },
+  })
+  const interaction = fakeInteraction()
+  await dynamic.execute(interaction)
+  assert.deepEqual(interaction.calls.map(([kind]) => kind), ['defer', 'edit'])
+})
+
+// "You do not have access to that" is about one member and belongs to one
+// member, whatever the command's usual privacy.
+test('a refusal is always private', async () => {
+  answers([definition()])
+  await dynamic.pull()
+  appInternal.dispatchCommand = async () => ({ ok: true, data: { ok: false, reason: 'forbidden' } })
+  const interaction = fakeInteraction()
+  await dynamic.execute(interaction)
+  assert.deepEqual(interaction.calls.map(([kind]) => kind), ['defer', 'delete', 'followUp'])
+  assert.equal(interaction.calls.at(-1)[1].ephemeral, true)
+})
+
 test('a refusal is phrased by the bot and edited into the deferred reply', async () => {
   answers([definition({ access: 'linked' })])
   await dynamic.pull()
@@ -204,7 +245,9 @@ test('a refusal is phrased by the bot and edited into the deferred reply', async
   const interaction = fakeInteraction()
   await dynamic.execute(interaction)
   assert.match(interaction.calls.at(-1)[1].content, /Link your Discord account/)
-  assert.equal(interaction.calls.filter(([kind]) => kind === 'edit').length, 1)
+  // Deferred ephemerally (access: 'linked'), so the refusal is one edit and no
+  // withdrawal — replying twice to a deferred interaction is what throws.
+  assert.deepEqual(interaction.calls.map(([kind]) => kind), ['defer', 'edit'])
 })
 
 test('an unreachable app is the same sentence to the member and a different line in the log', async () => {
@@ -214,6 +257,7 @@ test('an unreachable app is the same sentence to the member and a different line
   const interaction = fakeInteraction()
   await dynamic.execute(interaction)
   assert.match(interaction.calls.at(-1)[1].content, /Something went wrong/)
+  assert.equal(interaction.calls.at(-1)[1].ephemeral, true)
 })
 
 test('an interaction for a command the app no longer serves is left alone', async () => {