NoMethodError#message renders the receiver via its Ruby-level #name

[sisshiki1969]

Summary

Continues the ruby/spec compliance work (#891, #893, #894), closing the NoMethodError#message receiver-rendering gap in the core/exception category (CRuby 4.0.2 reference). Excluding the four spec files that Process.kill the runner itself, the category goes from 13 → 10 failures.

Change

CRuby builds a NoMethodError message by calling the receiver's — or, for an ordinary object, its class's — Ruby-level #name. So a class/module with an overridden def self.name shows that name rather than its anonymous #<Class:0x…> form. monoruby baked the message from the internal class name at raise time, which is wrong for that case.

The message is now rebuilt in the default method_missing handler (which has an Executor) for genuine undefined method errors:

• class / module receiver → class <#name> / module <#name> (anonymous → the #<Class:0x…> form);
• receiver with its own singleton class → its object string form (for #<Klass:0x…>);
• ordinary object → an instance of <class #name>.

The rendering goes through #name only, never #inspect (a spec asserts #inspect is not called during message building). Visibility errors (private/protected method … called) keep their own message and are excluded via an undefined flag, so only real missing-method errors are re-rendered (and carry #args).

Testing

• ruby/spec core/exception (minus kill-based files): 13 → 10 failures.
• New differential tests: tests/no_method_error_message.rs (4, comparing against CRuby — named class/module/instance, nil/true/false/Integer receivers, the no-#inspect guarantee, and unchanged private/protected messages).
• cargo test --lib --tests: green (a couple of transient LoadError/timeout flakes from concurrent build.rs reinstalls during local iteration, not from this change).

Remaining (out of scope here)

• Exception#backtrace second-element/format details and backtrace-array identity (~7 specs) and top-level cause printing (2) — both need backtrace-representation work.
• Signal-delivery-as-exception (Process.kill to self) — design decision in doc/signal_handling.md.

🤖 Generated with Claude Code

https://claude.ai/code/session_01XpzdoFu46d2ChJpSzeWsNK

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Generated by Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 97.91667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.49%. Comparing base (dc59098) to head (c387a60).

Files with missing lines	Patch %	Lines
monoruby/src/builtins/object.rs	97.91%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #895   +/-   ##
=======================================
  Coverage   90.48%   90.49%           
=======================================
  Files         189      189           
  Lines      123128   123170   +42     
=======================================
+ Hits       111416   111460   +44     
+ Misses      11712    11710    -2     

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