[Birfy]

Closes #888

Algorithm parameter values that declare choices now fold case and -/_ the same way parameter names already do (#876). --param sampling=sigmoid-novelty, archive_mode=KEEP_ALL, and mode=Linear resolve to the declared spelling, and algorithms run writes that canonical value into the spec. A close typo (novlty) ends with did you mean 'novelty'?; a nonsense value (greedy) still lists the choices and does not guess.

The fold lives in Param.coerce, so plan / MCP / plugin hosts inherit it too.

Verification

• pytest -q tests/test_algorithms.py tests/test_cli_algorithms_run.py tests/test_mcp_algorithm_spec.py tests/test_cli_algorithms_bare.py tests/test_changelog_fragments.py passed

[Birfy]

Verdict: PASS
Tip SHA: dacde8b

Ran: pytest -q tests/test_algorithms.py tests/test_cli_algorithms_run.py tests/test_mcp_algorithm_spec.py tests/test_cli_algorithms_bare.py tests/test_changelog_fragments.py at the tip → passed. resolve_params folds sigmoid-novelty / KEEP_ALL / Linear; novlty suggests novelty; greedy still lists choices with no guess.

risk_gate: T2 (94 lines / 5 files). No CHANGES REQUESTED. AGENT_PAUSE=false.

[Birfy]

Verdict: PASS
Tip SHA: dacde8b
Ran: pytest -q tests/test_algorithms.py tests/test_cli_algorithms_run.py tests/test_mcp_algorithm_spec.py tests/test_cli_algorithms_bare.py tests/test_changelog_fragments.py at the tip → passed.
Not run: full suite (CI covers 3.9–3.13).
risk_gate: T2 (94 lines / 5 files). No CHANGES REQUESTED. AGENT_PAUSE=false.

Correctness. Param.coerce now treats a string choice the same way parameter names already work (#876): if exactly one declared choice matches once case and -/_ are folded (_fold replaces - with _ after casefold), the value becomes that canonical spelling (sigmoid-novelty → sigmoid_novelty, KEEP_ALL → keep_all, Linear → linear). Two choices that fold together stay unresolved rather than guessed. A remaining unknown uses the same difflib.get_close_matches(_fold(value), named, n=1, cutoff=0.75) bar as parameter-name suggestions, so novlty ends with did you mean 'novelty'? while a nonsense value (greedy) still lists the choices and does not guess.

algorithm_override now stores {k: resolved[k] for k in params} after resolve_params, so algorithms run --param sampling=sigmoid-novelty writes the canonical value and only the user-supplied keys (defaults stay out of the spec). Because the fold lives in coerce, plan / MCP / plugin hosts inherit it without a second path.

Design. This is the natural counterpart of #876 / #874 / #882 / #884: names already folded, choice values did not. Putting the logic in Param.coerce rather than the CLI parser is the right layer — every caller that already validates types and choices gets the alias and the hint. Non-goals are respected (no space/punctuation folding, no change to what algorithms do with a canonical value).

Tests / docs. New resolve_params cases cover the #888 acceptance list (hyphen/case aliases on archive_selection.sampling, dgm.archive_mode, skillopt.mode; near-miss did you mean; greedy with no guess). CLI tests check that algorithms run --param sampling=sigmoid-novelty persists sigmoid_novelty and that sampling=novlty exits 2 with the hint and no leftover spec. Changelog fragment 888-param-choice-aliases.md is valid.

Risk. T2 by risk_gate.py (package validation only; 94 changed lines / 5 files, under the 250-line cap). No evolve-loop change. AGENT_PAUSE=false; will squash-merge when required CI is green.