fix: improve const-correctness in Expat.xs

[toddr-bot]

What

Fix const-correctness in Expat.xs by propagating const char * through internal helper functions.

Why

Expat callbacks receive const XML_Char * parameters, but newUTF8SVpv(), newUTF8SVpvn(), and append_error() took plain char *. This forced 30+ explicit (char *) casts throughout the file, silently discarding const qualifiers. Compilers couldn't catch accidental mutation of expat-owned strings.

How

• Changed newUTF8SVpv(), newUTF8SVpvn(), and append_error() to accept const char *
• Removed all 30+ now-unnecessary (char *) casts at call sites
• Replaced (char *) 0 with NULL (3 occurrences)
• Removed a redundant cast on the enc variable in XML_ParserCreate
• Left the one legitimate (char *) cast in the encoding loader (byte-level pointer arithmetic)

No functional change — the generated machine code is identical.

Testing

Full make test passes (59 programs, 677 subtests). Clean build with zero warnings.

🤖 Generated with Claude Code

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Quality Report

Changes: 1 file changed, 42 insertions(+), 42 deletions(-)

Code scan: clean

Tests: passed (OK)

Branch hygiene: clean

Generated by Kōan post-mission quality pipeline

[codecov]

Codecov Report

❌ Patch coverage is 95.23810% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.40%. Comparing base (4ee8e6f) to head (a621953).

Files with missing lines	Patch %	Lines
Expat/Expat.xs	95.23%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #254   +/-   ##
=======================================
  Coverage   76.40%   76.40%           
=======================================
  Files           1        1           
  Lines        1102     1102           
  Branches      346      346           
=======================================
  Hits          842      842           
  Misses         52       52           
  Partials      208      208           

Flag	Coverage Δ
perl	76.40% <95.23%> (ø)
xs	76.40% <95.23%> (ø)

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[toddr-bot]

Rebase with requested adjustments

Branch koan.toddr.bot/const-correctness was rebased onto main and review feedback was applied.

Stats

1 file changed, 42 insertions(+), 42 deletions(-)

Actions performed

• Already-solved check: negative (confidence=high, reasoning=None of the recent commits on main address const-correctness in Expat.xs — the commits cover unrelat)
• Resolved merge conflicts (1 round(s))
• Rebased koan.toddr.bot/const-correctness onto origin/main
• Pre-push CI check: previous run passed
• Force-pushed koan.toddr.bot/const-correctness to origin
• CI check enqueued in ## CI (async)

CI status

CI will be checked asynchronously.

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