Adds tethys run express mode

[Copilot]

⚠️ Read this first

This is an AI-generated proof of concept. The design and implementation were produced with an AI assistant (Claude) working interactively with @gagelarsen, then verified end-to-end locally. It is a draft for discussion with the Tethys team — not a request to merge as-is. All suggestions, redesigns, and pushback are welcome.

Implements #1286.

What this does

tethys run app.py [-p PORT] [--host HOST] [--no-browser] [--no-reload] [--clean]

Runs a bare, single-file component app — never pip-installed, no pyproject.toml, no portal config, no database setup, no login — with the ergonomics of shiny run / streamlit run:

# app.py — complete and runnable
from tethys_sdk.components import ComponentBase

class App(ComponentBase):
    name = "My Dashboard"

@App.page
def home(lib):
    return lib.tethys.Display(lib.tethys.Map())

First run takes ~4s (silent SQLite migration); subsequent runs ~3s. Hot reload is on by default (Django's stock autoreloader — the app file is an imported module). tethys run with no argument looks for app.py in the cwd.

How it works (design)

"Portal-in-a-box": the existing portal runtime runs unmodified, configured down via an ephemeral generated environment — chosen over (a) a purpose-built minimal runtime (dual-runtime drift risk) and (b) materializing the file into a generated package (codegen indirection). Because everything downstream is stock machinery, an express app is guaranteed to behave identically when later installed in a real portal — the same file drops verbatim into a scaffolded component app's app.py (a future tethys scaffold --from app.py could automate graduation).

1. tethys_cli/run_commands.py (new): validates the file (AST check for a ComponentBase subclass), creates ~/.tethys/express/<pkg>_<hash-of-abs-path>/ as an isolated TETHYS_HOME, writes a portal_config.yml into it (MULTIPLE_APP_MODE: False, STANDALONE_APP: <pkg>, ENABLE_OPEN_PORTAL: True, persisted SECRET_KEY), runs manage.py migrate --no-input (idempotent, every start), then execs manage.py runserver. Configuration flows through env vars (TETHYS_HOME, TETHYS_EXPRESS_APP) so it survives autoreloader restarts. No changes to settings.py were needed.
2. tethys_apps/base/express.py (new): when TETHYS_EXPRESS_APP is set, loads the file as tethysapp.<pkg>.app and pre-registers it (plus a synthetic parent package) in sys.modules, so the untouched harvester/register_controllers machinery — including its importlib.reload() — resolves it like an installed app. Missing metadata is synthesized: package/root_url from the filename (parent dir for generic app.py), name title-cased, index = first @App.page function.
3. tethys_apps/harvester.py (~10 lines): include the express app in the harvest dict.
4. tethys_apps/base/component_base.py: __init_subclass__ hook calls the metadata synthesis at class-definition time — required because @App.page reads app.package at decoration time (ComponentLibrary keying).

Drive-by bug fixes (pre-existing, single-app mode)

Both were hit during testing and affect non-express portals too — happy to split them into a separate PR:

• tethys_apps/utilities.py: get_configured_standalone_app() caught Postgres's ProgrammingError but not SQLite's OperationalError, so a fresh single-app portal with reactpy_django installed crashed during migrate (reactpy's app-ready hook imports the URLconf, which queries TethysApp before tables exist).
• tethys_apps/base/component_base.py: auto nav links hard-coded /apps/<root_url>/, which 404s when MULTIPLE_APP_MODE=False (apps are served at root). Now settings-aware.

Verification performed

• 28 new unit tests (test_express.py, test_run_commands.py) — all passing; regression run of touched-module test files shows failure sets identical to main (3 pre-existing, unrelated).
• End-to-end in a real browser (Playwright): page renders, button click round-trips state over the ReactPy websocket, multi-page nav works, hot reload verified by editing the file mid-serve.
• Built a real dashboard app on it (Utah lakes map + click-for-fish-species from public APIs) as a dogfooding exercise.
• flake8 and black --check clean.

Known limitations / open questions

• Component apps only (no classic template apps) — intentional for v1.
• Hard-wired anonymous (ENABLE_OPEN_PORTAL); no auth flag yet.
• Multi-file express apps work incidentally (sibling controllers.py etc. are importable via the synthetic package path) but are untested/undocumented.
• The generated state dir accumulates under ~/.tethys/express/ (per-app, keyed by file path; --clean wipes one app's state). No global GC.
• requests/network access to esm.sh (React CDN) is required at page load, as with all component apps.
• Naming (tethys run vs tethys express), the state-dir lifecycle, and whether portal-in-a-box is the right long-term architecture are all up for debate in Feature proposal: tethys run app.py — zero-config single-file app runner ("Tethys Express") #1286.

🤖 Generated with Claude Code

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Co-Pilot Additions

Description

This merge request hardens the existing tethys run express-mode flow for Component Apps without expanding scope beyond the v1 design. It addresses the open review feedback, makes localhost-only serving the documented default, and closes edge cases that previously failed with confusing import/runtime errors.

Changes Made to Code

• CLI hardening

  • Validates explicit and derived express package names before bootstrapping the app environment.
  • Converts invalid-name failures into direct CLI errors instead of later module import crashes.
  • Warns when --host is set to a non-loopback address because express mode runs with DEBUG=True and ENABLE_OPEN_PORTAL=True.

• Express loader robustness

  • Normalizes derived package names more defensively and rejects empty / non-identifier results.
  • Reads app source as UTF-8 during discovery for deterministic parsing across environments.
  • Initializes the synthetic tethysapp namespace as a proper package and checks module spec/loader creation before execution.

• Docs

  • Documents 127.0.0.1 as the default bind address.
  • Adds a clear warning that non-localhost binding is an explicit opt-in and should only be used on trusted networks.
  • Updates release notes to reflect the safer host default.

• Focused test coverage

  • Adds coverage for invalid derived filenames, invalid explicit package values, missing runtime dependency handling, loopback/non-loopback host detection, warning emission, UTF-8 source reads, and express loader spec failures.
  • Keeps express harvesting tests isolated from unrelated Django runtime setup.

Example of the supported explicit override for filenames that would not derive a valid package cleanly:

from tethys_sdk.components import ComponentBase

class App(ComponentBase):
    package = "my_dashboard"

Related PRs, Issues, and Discussions

• PR [WIP] Add tethys run — zero-config single-file app runner (express mode POC) #1287
• Issue Feature proposal: tethys run app.py — zero-config single-file app runner ("Tethys Express") #1286
• Open review comments on express-mode validation and host exposure

Additional Notes

• Scope remains Component Apps only.
• Standalone/single-app routing behavior is unchanged; the cleanup here focuses on validation, safety messaging, and review-readiness.

Quality Checks

• At least one new test has been written for new code
• New code has 100% test coverage
• Code has been formatted with Black
• Code has been linted with flake8
• Docstrings for new methods have been added
• The documentation has been updated appropriately

[Copilot]

🟡 Changes recommended

Unresolved package/path and host-exposure findings, plus encoding and regression-test gaps, block approval.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Polishes tethys run express mode for Component Apps with safer host handling, stronger package validation, robust loading, and focused documentation/tests.

Changes:

• Hardens express CLI setup and runtime safety.
• Improves synthetic app discovery, metadata, and routing.
• Adds focused tests and updates documentation and release notes.

File summaries

File	Reviewed changes	Final review notes
tethys_cli/run_commands.py	Express CLI workflow and server startup	Critical (2 votes, line 103): validate explicit packages before path construction. Critical (3 votes, line 141): warn for non-loopback hosts.
tethys_cli/__init__.py	Registers the run command	—
tethys_apps/utilities.py	Handles SQLite startup errors	Moderate (3 votes, line 685): add OperationalError regression coverage.
tethys_apps/harvester.py	Harvests express apps	—
tethys_apps/base/express.py	Loads and synthesizes express apps	Moderate (3 votes, lines 45/198): read source explicitly as UTF-8. Moderate (1 vote, line 77): validate normalized identifiers. Critical (1 vote, line 100): validate explicit package names.
tethys_apps/base/component_base.py	Adds metadata and root routing	Moderate (3 votes, line 69): test the MULTIPLE_APP_MODE=False navigation branch.
tests/unit_tests/test_tethys_cli/test_run_commands.py	CLI test coverage	—
tests/unit_tests/test_tethys_apps/test_base/test_express.py	Express loader test coverage	—
docs/whats_new.rst	Release-note entry	—
docs/tethys_sdk/components.rst	Express-mode guidance	—
docs/tethys_cli/run.rst	Run-command documentation	Nit (3 votes, line 73): warn about non-localhost exposure. Nit (3 votes, line 40): qualify the full-portal graduation claim.
docs/tethys_cli.rst	Includes run-command documentation	—

Review details

Suppressed comments (2)

tethys_apps/base/express.py:199

• spec_from_file_location can return None for a file without a supported Python suffix, or a spec without a loader, but both are passed straight into module_from_spec/exec_module. Check these results first so unsupported inputs produce a controlled loader error instead of an AttributeError/TypeError during harvesting.

    module_spec = spec_from_file_location(module_name, app_file)
    module = module_from_spec(module_spec)

tethys_apps/base/express.py:78

• This normalization does not guarantee a valid Python identifier for Unicode names; for example, ².py produces app_², for which isidentifier() is false. That value is then used for the synthetic module and generated state path, so the claimed invalid-derived-name validation is still missing. Validate the final normalized name as nonempty and isidentifier() before returning it, and surface the failure through the CLI.

    package = re.sub(r"\W", "_", _source_stem(app_file)).lower()
    if package[0].isdigit():

• Files reviewed: 12/12 changed files
• Comments generated: 8
• Review effort level: Lite

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[swainn]

@shawncrawley and @gagelarsen I had co-pilot try to clean this up and tie up loose ends. Can you test it to make sure it still works?