fix: use strings.Cut to resolve stringscut lint violation in known_needs_expressions

[Copilot]

golangci-lint was failing CI with stringscut: strings.Index can be simplified using strings.Cut in pkg/workflow/known_needs_expressions.go:145.

Change

Replaced the strings.Index + manual slice pattern with the idiomatic strings.Cut:

// Before
dotIdx := strings.Index(rest, ".")
if dotIdx < 0 { ... }
jobName := rest[:dotIdx]

// After
jobName, _, ok := strings.Cut(rest, ".")
if !ok { ... }

Original prompt

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This section details on the original issue you should resolve

<issue_title>[CI Failure Doctor] Investigate lint-go stringscut failure</issue_title>
<issue_description>### CI Failure Investigation - Run github/gh-aw#37390

Summary

golangci-lint failed in the lint-go job because pkg/workflow/known_needs_expressions.go still splits a needs.* expression with strings.Index, which triggers the modernize stringscut rule.

Failure Details

• Run: 22278268173
• Commit: c99d014
• Trigger: push

Root Cause Analysis

The lint-go job runs make golint, which invokes golangci-lint with the modernize suite that includes the stringscut check. The log shows pkg/workflow/known_needs_expressions.go:145:13: stringscut: strings.Index can be simplified using strings.Cut, so the linter exits with code 2 before any other checks run.

Failed Jobs and Errors

• lint-go – pkg/workflow/known_needs_expressions.go:145:13: stringscut: strings.Index can be simplified using strings.Cut (modernize)

Investigation Findings

• Running make golint locally reproduces the failure because the stringscut rule is enabled by default in the lint configuration.
• Swapping the strings.Index call for strings.Cut eliminates the warning without affecting the existing logic that drops post-activation needs expressions.
• Attempts to run make fmt on the tree fail because go fmt ./... wants Go 1.25.0 but the download from proxy.golang.org is blocked, and forcing GOTOOLCHAIN=local runs against Go 1.24.12, which is below the module's go 1.25 requirement.

Recommended Actions

• Re-run make golint on main after merging this change to confirm no other stringscut violations remain.

Prevention Strategies

Use strings.Cut (or other modern splitting helpers) whenever slicing needs.* expressions so the stringscut lint rule stays satisfied across the codebase.

AI Team Self-Improvement

Always prefer the Go 1.21+ helpers (e.g., strings.Cut) for substring extraction so modernization rules like stringscut do not break CI.

Historical Context

No prior CI Failure Doctor investigations matched this stringscut violation pattern.

🩺 Diagnosis provided by CI Failure Doctor

To install this workflow, run gh aw add githubnext/agentics/workflows/ci-doctor.md@ea350161ad5dcc9624cf510f134c6a9e39a6f94d. View source at https://github.com/githubnext/agentics/tree/ea350161ad5dcc9624cf510f134c6a9e39a6f94d/workflows/ci-doctor.md.

• expires on Feb 23, 2026, 1:48 PM UTC

Comments on the Issue (you are @copilot in this section)

• Fixes [CI Failure Doctor] Investigate lint-go stringscut failure #17726

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Pull request overview

Updates known_needs_expressions parsing to satisfy golangci-lint’s modernize(stringscut) rule by replacing a strings.Index + slicing pattern with strings.Cut, preserving the existing behavior for malformed needs.* expressions.

Changes:

• Replace strings.Index(rest, ".") + manual slicing with strings.Cut(rest, ".") in filterExpressionsForActivation.

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