refactor(strconv): raise structured StrConvError from internal/strconv

[bobzhang]

Summary

Follow-up to the discussion on #3996: internal/strconv raised bare Failure with magic message strings ("value out of range", "invalid syntax", "invalid base"), so callers could only catch-all or string-compare. This introduces a structured error and threads it through every consumer, with zero externally visible changes.

pub(all) suberror StrConvError {
  RangeError
  SyntaxError
  InvalidBase
} derive(Eq, @debug.Debug)

All parse_* signatures (public and the private call chain) now declare raise StrConvError, and a message() method carries the historical strings.

Consumers

• json (lex_number.mbt): both sentinel fallbacks now catch RangeError precisely; SyntaxError | InvalidBase become abort("unreachable") — the lexer has already validated the number grammar, so a strconv disagreement is a bug that should surface loudly instead of being silently laundered into Number(Infinity, repr=...).
• json (from_json.mbt): Int64/UInt64 decoding interpolates err.message(), keeping the exact historical JsonDecodeError texts.
• string: the pub using @internal/strconv { parse_* } re-export becomes thin wrappers that translate StrConvError back into Failure with the historical messages. External users of @string.parse_* see identical behavior — the existing snapshot tests pinning Failure("value out of range") pass unchanged.

Why not let the typed error escape through @string.parse_*?

The type lives in an internal package, so external users could never name its constructors to match on it — they'd actually lose the ability to match Failure(msg) they have today. Translation at the facade keeps the public contract intact; giving external users a typed error would mean unifying with the public strconv package's (separate, also stringly) StrConvError, which is a bigger, breaking discussion.

Validation

• internal/strconv + json: 228/228; string: all passing
• moon info: string/pkg.generated.mbti and json/pkg.generated.mbti byte-identical; only internal/strconv/pkg.generated.mbti (not publicly exposed) changed
• moon fmt clean

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Refactors internal/strconv to raise a structured StrConvError (instead of Failure with magic strings) and threads that typed error through in-module consumers, while preserving the public @string.parse_* error contract by translating back to Failure("<historical message>").

Changes:

• Introduces StrConvError (RangeError | SyntaxError | InvalidBase) in internal/strconv and updates all parse helpers to raise StrConvError.
• Updates json number lexing/decoding to handle out-of-range vs. syntax/base errors precisely (range → infinity sentinel; others treated as unreachable given lexer validation).
• Replaces string’s direct pub using @internal/strconv { parse_* } re-exports with thin wrappers that map StrConvError back to legacy Failure messages.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
string/strconv.mbt	Adds wrapper functions that catch @internal/strconv.StrConvError and re-raise legacy Failure messages to keep the public contract stable.
json/lex_number.mbt	Narrows error handling from catch-all to RangeError vs. other StrConvError variants when falling back to @internal/strconv.parse_double.
json/from_json.mbt	Updates Int64/UInt64 decoding to interpolate StrConvError::message() to preserve historical error text.
internal/strconv/strconv_errors.mbt	Defines StrConvError and helper raisers (range_err, syntax_err, base_err) plus message() for legacy strings.
internal/strconv/strconv_int.mbt	Updates integer parsing helpers/signatures/tests to raise and assert StrConvError variants.
internal/strconv/strconv_uint.mbt	Updates unsigned parsing signatures/tests to raise and assert StrConvError variants.
internal/strconv/strconv_double.mbt	Updates double parsing signature/tests to raise and assert StrConvError variants, especially overflow as RangeError.
internal/strconv/strconv_decimal.mbt	Adjusts decimal parsing signatures and updates tests to expect StrConvError (including debug inspection of RangeError).
internal/strconv/strconv_number.mbt	Updates internal number parsing helper signatures/docs to raise StrConvError.
internal/strconv/strconv_bool.mbt	Updates boolean parsing signature/tests to raise and assert StrConvError variants.
internal/strconv/strconv_coverage_test.mbt	Updates coverage tests to treat StrConvError variants as the expected failure modes without string matching.
internal/strconv/moon.pkg	Switches dependencies from error to debug to support derived @debug.Debug for StrConvError.
internal/strconv/pkg.generated.mbti	Regenerates the internal package interface to reflect raise StrConvError signatures and exported error/methods.

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