feat: projects command — find the project IDs the config is missing

Reading gizmo_id during normalization fixed attribution, but it cannot
answer "which projects am I missing?": normalization only runs on
conversations being exported, and a normal run skips everything already
cached. Discovering the gaps would have meant --force re-exporting the
whole archive.

`ai-chat-exporter projects` does it directly. It lists conversations,
collects the g-p- ids they belong to, resolves display names, and prints a
table marking which are absent from .env plus a paste-ready
CHATGPT_PROJECT_IDS line. --write applies it; --deep falls back to one
detail request per conversation when the listing does not carry gizmo_id
(unverified which shape this account returns, so the command reports which
path it took rather than assuming).

This matters beyond tidiness: attribution is now self-correcting, but the
listing pass still needs the ids. Conversations that live only inside a
project never appear in the default listing, so an unlisted project's chats
are not merely misfiled — they are never fetched.

6 CLI tests: reporting, the already-configured case, the g-p- guard, --deep,
the hint when --deep is needed, and --write. 324 pass.

tests/test_cli.py

@@ -1,5 +1,7 @@
 """CLI-level tests using Click's CliRunner — no live API calls required."""
 
+from pathlib import Path
+
 import pytest
 from click.testing import CliRunner
 
@@ -297,3 +299,119 @@ class TestCanaryCommand:
         )
         assert result.exit_code == 1
         assert "No web-API provider tokens" in result.output
+
+
+class TestProjectsCommand:
+    """`projects` discovers project IDs missing from CHATGPT_PROJECT_IDS."""
+
+    def _patch_provider(self, monkeypatch, summaries, details=None, names=None):
+        import src.providers.chatgpt as chatgpt_mod
+
+        names = names or {}
+        details = details or {}
+
+        class FakeProvider:
+            def __init__(self, **kwargs):
+                self._project_ids = kwargs.get("project_ids") or []
+
+            def fetch_all_conversations(self, since=None):
+                return summaries
+
+            def get_conversation(self, conv_id):
+                return details.get(conv_id, {})
+
+            def _fetch_project_name(self, gizmo_id):
+                return names.get(gizmo_id, gizmo_id)
+
+        monkeypatch.setattr(chatgpt_mod, "ChatGPTProvider", FakeProvider)
+        return FakeProvider
+
+    def _env(self, tmp_path, **extra):
+        # Clears the ToS gate and the first-run doctor check.
+        cache = Cache(tmp_path)
+        cache.acknowledge_tos()
+        cache.mark_exported("chatgpt", "dummy", {"updated_at": "2024-01-01T00:00:00Z"})
+        env = {
+            "CHATGPT_SESSION_TOKEN": "eyJtesttoken",
+            "CACHE_DIR": str(tmp_path),
+            "EXPORT_DIR": str(tmp_path / "exports"),
+        }
+        env.update(extra)
+        return env
+
+    def test_reports_project_absent_from_config(self, tmp_path, monkeypatch):
+        self._patch_provider(
+            monkeypatch,
+            summaries=[{"id": "c1", "gizmo_id": "g-p-missing"}],
+            names={"g-p-missing": "Tech Questions"},
+        )
+        result = CliRunner(mix_stderr=True).invoke(
+            cli, ["--no-log-file", "projects"], env=self._env(tmp_path)
+        )
+        assert result.exit_code == 0
+        assert "Tech Questions" in result.output
+        assert "g-p-missing" in result.output
+        assert "CHATGPT_PROJECT_IDS=g-p-missing" in result.output
+
+    def test_quiet_when_everything_is_configured(self, tmp_path, monkeypatch):
+        self._patch_provider(
+            monkeypatch,
+            summaries=[{"id": "c1", "gizmo_id": "g-p-known"}],
+            names={"g-p-known": "Known"},
+        )
+        result = CliRunner(mix_stderr=True).invoke(
+            cli,
+            ["--no-log-file", "projects"],
+            env=self._env(tmp_path, CHATGPT_PROJECT_IDS="g-p-known"),
+        )
+        assert result.exit_code == 0
+        assert "already configured" in result.output
+
+    def test_custom_gpt_ids_are_ignored(self, tmp_path, monkeypatch):
+        self._patch_provider(
+            monkeypatch,
+            summaries=[{"id": "c1", "gizmo_id": "g-notaproject"}],
+        )
+        result = CliRunner(mix_stderr=True).invoke(
+            cli, ["--no-log-file", "projects"], env=self._env(tmp_path)
+        )
+        assert "g-notaproject" not in result.output
+
+    def test_deep_reads_conversation_details(self, tmp_path, monkeypatch):
+        self._patch_provider(
+            monkeypatch,
+            summaries=[{"id": "c1"}],  # listing carries no gizmo_id
+            details={"c1": {"gizmo_id": "g-p-fromdetail"}},
+            names={"g-p-fromdetail": "Found Deep"},
+        )
+        result = CliRunner(mix_stderr=True).invoke(
+            cli, ["--no-log-file", "projects", "--deep"], env=self._env(tmp_path)
+        )
+        assert "Found Deep" in result.output
+        assert "CHATGPT_PROJECT_IDS=g-p-fromdetail" in result.output
+
+    def test_without_deep_says_so_rather_than_reporting_nothing(self, tmp_path, monkeypatch):
+        self._patch_provider(
+            monkeypatch,
+            summaries=[{"id": "c1"}],
+            details={"c1": {"gizmo_id": "g-p-fromdetail"}},
+        )
+        result = CliRunner(mix_stderr=True).invoke(
+            cli, ["--no-log-file", "projects"], env=self._env(tmp_path)
+        )
+        assert "--deep" in result.output
+
+    def test_write_updates_env(self, tmp_path, monkeypatch):
+        self._patch_provider(
+            monkeypatch,
+            summaries=[{"id": "c1", "gizmo_id": "g-p-new"}],
+            names={"g-p-new": "New Project"},
+        )
+        runner = CliRunner(mix_stderr=True)
+        with runner.isolated_filesystem(temp_dir=tmp_path) as fs:
+            result = runner.invoke(
+                cli, ["--no-log-file", "projects", "--write"], env=self._env(tmp_path)
+            )
+            assert result.exit_code == 0
+            env_text = (Path(fs) / ".env").read_text(encoding="utf-8")
+            assert "CHATGPT_PROJECT_IDS=g-p-new" in env_text