fix(injector): resolve .AST.Fun.Name crash on SelectorExpr in wrap-expression templates

[eliottness]

What does this PR do?

Fixes a build crash (can't evaluate field Name in type dst.Expr) that occurs when a function-call join-point matches a qualified call like http.Get(...) and the advice template accesses {{ .AST.Fun.Name }}.

Root cause: proxyCallExpr.Fun() returns dst.Expr (interface). When the underlying node is a *dst.SelectorExpr (e.g., for http.Get), proxySelectorExpr had no Name field or method. Go's text/template could not resolve .Name, crashing with the error above. The same template works fine for bare/dot-imported calls (Get(...)) where Fun is a *dst.Ident with a promoted Name field.

Fix: Add a Name() string method to proxySelectorExpr in a hand-written companion file (dot_ast_extras.go) that returns Sel.Name. This makes {{ .AST.Fun.Name }} work transparently for both node types without any changes to dd-trace-go templates — fully backwards compatible.

Motivation

Customer escalation APMS-19232: any user calling http.Get(...), http.Head(...), http.Post(...), or http.PostForm(...) in a function with a context.Context parameter fails to build with orchestrion. The dd-trace-go net/http client aspect (Get|Head|Post|PostForm) triggers the crash.

Describe how you validated your changes

• Added end-to-end injector regression test selector-expr-fun-name/ that exercises exactly the failure path: a function-call join-point on net/http.Get with input code that has a context.Context parameter, forcing the template branch that evaluates {{ .AST.Fun.Name }} on a *dst.SelectorExpr
• All injector tests pass: go test ./internal/injector/... (14 packages, 51s)
• golangci-lint clean

Additional Notes

The fix lives in dot_ast_extras.go, a hand-written companion to the auto-generated dot_ast.proxies.go. This separation keeps generated code untouched while allowing targeted extensions. A comment in the new file guides future maintainers to add similar extensions there.

The alternative (adding a new FuncName() template helper) was rejected because it would require dd-trace-go to depend on a minimum orchestrion version, breaking backwards compatibility.

[datadog-datadog-prod-us1-2]

🎯 Code Coverage (details)
• Patch Coverage: 0.00%
• Overall Coverage: 67.89%

_{This comment will be updated automatically if new data arrives.
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[eliottness]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 👍

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.66%. Comparing base (e061d12) to head (fa2c920).
⚠️ Report is 77 commits behind head on main.

Files with missing lines	Patch %	Lines
...rnal/injector/aspect/advice/code/dot_ast_extras.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #819      +/-   ##
==========================================
+ Coverage   65.72%   69.66%   +3.94%     
==========================================
  Files         113      117       +4     
  Lines        7926     6902    -1024     
==========================================
- Hits         5209     4808     -401     
+ Misses       2192     1545     -647     
- Partials      525      549      +24     

Components	Coverage Δ
Generators	83.23% <ø> (+2.98%)	⬆️
Instruments	∅ <ø> (∅)
Go Driver	75.58% <65.38%> (-0.23%)	⬇️
Toolexec Driver	74.78% <100.00%> (+7.25%)	⬆️
Aspects	76.89% <75.00%> (+4.98%)	⬆️
Injector	77.19% <76.41%> (+4.39%)	⬆️
Job Server	68.38% <55.55%> (+2.46%)	⬆️
Other	69.66% <65.11%> (+3.94%)	⬆️

Files with missing lines	Coverage Δ
...rnal/injector/aspect/advice/code/dot_ast_extras.go	0.00% <0.00%> (ø)

... and 108 files with indirect coverage changes

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