[Code Quality] Investigate and address January 2026 agent success rate decline

[github-actions]

Description

Analysis of 4,389 copilot agent tasks shows a concerning decline in success rates during January 2026. Success rate dropped from 76.2% in November 2025 to 64.8% in January 2026 - an 11.4 percentage point decrease.

Trend Data

Month	Tasks	Success Rate	Change
Oct 2025	397	73.3%	baseline
Nov 2025	884	76.2%	+2.9% ✅
Dec 2025	1,348	71.6%	-4.6% ⚠️
Jan 2026	1,760	64.8%	-11.4% 🚨

Impact

• ~200 additional failed tasks in January compared to November baseline
• Consistent downward trend since November peak
• Affects all task types - not isolated to one category

Investigation Areas

1. Recent Agent Instruction Changes

• Review changes to agent prompts in December-January
• Check for new constraints or guidelines that may be too restrictive
• Analyze prompt length and complexity trends

2. Infrastructure Changes

• Check for GitHub Actions runner updates
• Review MCP server availability and performance
• Analyze network/timeout issues

3. Task Complexity Increase

• Compare average files changed per task over time
• Analyze commit count trends
• Review task description length and clarity

4. Tooling Changes

• Check for linter/formatter updates
• Review dependency version changes
• Analyze tool availability issues

Proposed Investigation Steps

1. Data Analysis (Day 1)

   • Pull detailed metrics for Nov 2025 vs Jan 2026
   • Compare task types, complexity, and failure patterns
   • Identify specific failure categories driving the decline

2. Code Review (Day 2)

   • Review commits between Nov-Jan affecting agent behavior
   • Check for prompt changes, validation changes, tool updates
   • Identify configuration changes

3. Root Cause Analysis (Day 3)

   • Correlate changes with success rate drops
   • Test hypothesis with sample task replays
   • Document findings with evidence

4. Remediation Plan (Day 3)

   • Propose specific fixes based on root cause
   • Prioritize by impact
   • Create follow-up issues for implementation

Success Criteria

• Root cause(s) identified with supporting data
• Correlation between changes and success rate decline established
• Remediation plan with specific action items created
• Follow-up issues created for each fix
• Success rate returns to >70% baseline within 2 weeks of fixes

Priority

Critical - 11.4% decline affects hundreds of tasks and project velocity

Source

Extracted from Copilot Agent Prompt Clustering Analysis - January 2026

Estimated Effort

3-5 days - Requires comprehensive investigation across multiple areas

Data Sources

• Discussion [prompt-clustering] 🔬 Copilot Agent Prompt Clustering Analysis - January 2026 #12473 - Prompt clustering analysis with temporal trends
• Session logs from Nov 2025 - Jan 2026
• GitHub Actions workflow run history
• Agent prompt version history

Follow-up Required

This is an investigation task that will likely spawn multiple implementation tasks once root causes are identified.

AI generated by Discussion Task Miner - Code Quality Improvement Agent

• expires on Feb 12, 2026, 9:15 AM UTC