v0.4.0 — Path A first break (P0.9 dependency split + P0.10 friendly error)

The single break release of the Path A P0 plan
(see docs/design/path-a-roadmap.md §3.2). The break is a packaging
change only — no public Python API is renamed, removed, or signature-
changed. The "no-change" upgrade line is pip install 'agentao[full]',
which reproduces the 0.3.x bundled closure exactly (CI-enforced against
a 122-package baseline).

Breaking changes

• P0.9 dependency split — pip install agentao now installs only
  the core (7 packages) needed to construct an Agentao() instance and
  call chat() against an OpenAI-compatible endpoint. CLI, web fetch,
  and Chinese tokenization become opt-in extras.

  0.3.x direct dep	0.4.0 location
  openai / httpx / pydantic / pyyaml / mcp / python-dotenv / filelock	core
  rich / prompt-toolkit / readchar / pygments	[cli]
  beautifulsoup4	[web]
  jieba	[i18n]

  Migration matrix:

  You are…	Install line
  Embedding host (Python from agentao import Agentao)	pip install agentao
  CLI user (agentao console script)	pip install 'agentao[cli]'
  Want zero behaviour change	pip install 'agentao[full]'

  Closure equivalence is enforced by tests/test_dependency_split.py
  against tests/data/full_extras_baseline.txt (122 packages frozen
  on 2026-05-01). See docs/migration/0.3.x-to-0.4.0.md for the full
  guide.

Added

• P0.10 friendly missing-dep error — running the agentao CLI in
  a core-only install (no [cli] extra) now exits 2 with a one-line
  actionable message instead of crashing with an opaque
  ModuleNotFoundError: rich:

  agentao CLI requires extra packages (missing: rich).
    pip install 'agentao[cli]'   # CLI surface only
    pip install 'agentao[full]'  # 0.3.x-equivalent closure
  See docs/migration/0.3.x-to-0.4.0.md for details.
  

  Implementation: agentao/cli/__init__.py defines entrypoint()
  inline (no module-level imports of rich / prompt_toolkit / readchar /
  pygments) so the module load itself stays free of CLI deps; every
  [cli] dep is preflighted via importlib.util.find_spec so a
  partial install (rich present, prompt_toolkit missing) still hits
  the friendly path instead of leaking a "Fatal error" from
  entrypoints.run_init_wizard's broad except Exception. All other
  public names in agentao.cli lazy-load via PEP 562 __getattr__.
  Slow-marked tests in tests/test_cli_missing_dep_message.py cover
  the friendly-message path, the post-[cli] boot path, the
  no-trace-leak invariant, and the partial-install regression.

• docs/migration/0.3.x-to-0.4.0.md — full migration guide with
  install matrix, dependency map, common project-shape recipes, and
  a [full] fallback for any path the migration may have missed.

Changed

• Web tools omitted from the registry without [web] —
  WebFetchTool and WebSearchTool register only when
  beautifulsoup4 is importable. In a core install the model never
  sees web_fetch / web_search in its tool schema (vs. the previous
  behaviour of registering them and failing at execute time with an
  opaque ImportError). Mirrors the existing bg_store is not None
  pattern that already conditionally registers the background-agent
  tools.

• Memory recall degrades gracefully without [i18n] —
  MemoryRetriever.tokenize() skips the jieba code path entirely
  when the query has no CJK characters (cheap regex check). On a
  CJK-bearing query in a [i18n]-less install, _cjk_segment()
  returns an empty set with a one-time warning pointing at
  pip install 'agentao[i18n]' instead of silently failing.

• CI test environment installs [cli,web,i18n] — the existing
  unit-test surface imports from agentao.cli import AgentaoCLI,
  the web-fetch tool, and the jieba memory path. The default Test
  matrix job now installs those three extras so the suite still
  resolves in the core-split world. The core-only contract is
  independently validated by the smoke job and
  tests/test_dependency_split.py.

• Shared test helper tests/support/wheel.py — REPO_ROOT,
  find_wheel(), require_wheel(), and make_venv() centralized
  out of the venv-creation pattern that was duplicated across
  test_clean_install_smoke.py, test_dependency_split.py, and
  test_cli_missing_dep_message.py.