fix(workflow): stop losing widget input on Streamlit < 1.50

[t0mdavid-m]

src/workflow/StreamlitUI.py is template code. The identical patch is
proposed upstream in OpenMS/streamlit-template#402 — the two diffs are
byte-identical, so a later template sync will not conflict.

Problem

Selecting multiple mzML files in the workflow configure page silently loses
some of them: select six files, only three stick — every second click is
discarded, and the file visibly pops back out of the box.

Root cause

StreamlitUI._input_widget_impl feeds the persisted parameter back into every
widget as its initial-value argument:

value = self.params[key]
st.multiselect(name, options=options, default=value, key=key, ...)

On Streamlit < 1.50 that argument is hashed into the widget's element id
(compute_and_register_element_id(..., default=default_values, ...)). So each
interaction changed default → changed the element id → the browser's next
interaction arrived filed under the previous id, the lookup fell through to
the prior run's value, and that interaction was silently dropped.

Streamlit 1.50.0 changed exactly this, with the comment "Treat the provided
key as the main identity. Only include changes to the options, accept_new_options,
and max_selections in the identity computation as those can invalidate the current
selection." — default was removed from the id. So ≥ 1.50 was never affected.

This is not multiselect-specific. On 1.43.0 every widget type hashes its
current value into the id (text_widgets/checkbox/slider/number_input
hash value=, selectbox hashes index=), so the fix is applied uniformly.

Fix

Seed a widget only on its first render. Streamlit already ignores the
initial-value argument once a keyed widget has an entry in session state, so
this is behaviour-preserving — it just stops the id from churning:

def seed(**kwargs: Any) -> dict:
    return {} if key in st.session_state else kwargs

st.multiselect(name, options=options, key=key, ..., **seed(default=value))

This is consistent with how the codebase already works: apply_preset()
deletes the affected session keys ("so widgets re-initialize fresh") and
clear_parameter_session_state() exists for the same purpose. Reloading from
params.json still works because those paths clear session state first.

Also sorts the select_input_file options — path.iterdir() is unordered, so
both the displayed order and (on < 1.50) the element id varied between restarts.

Verification

Driven against the real StreamlitUI._input_widget_impl and the real
ParameterManager, on streamlit 1.49.1 (the pinned version):

before (main):  6 clicked -> 3 STICK: ['A.mzML', 'C.mzML', 'E.mzML']
after  (patch): 6 clicked -> 6 STICK: all six

Regression-tested across text, number (int and float), checkbox,
selectbox, slider and multiselect — first-render seeding, reload from
params.json, and persisted value type all unchanged, on both 1.49.1 and
1.53.1.

Test suite shows no change: failures/errors are byte-identical before and
after the patch (they are pre-existing, from missing example data).

	before	after
streamlit-template	4 failed, 164 passed, 4 skipped	4 failed, 164 passed, 4 skipped
quantms-web	6 failed, 80 passed, 2 skipped, 4 errors	6 failed, 80 passed, 2 skipped, 4 errors

Note on the pin

requirements.txt pins streamlit==1.49.1, which is on the affected side of
the 1.50 boundary — so this bug is live on main today. This fix is
version-independent and does not require bumping the pin, but bumping to
>=1.50 would be worthwhile separately as defence in depth.

🤖 Generated with Claude Code

https://claude.ai/code/session_016Qn3mLqr7zBr7rgCokx6ku

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