Systems Architecture Nov 1, 2025 12 min read

From Traditional Developer to Systems Architect: The 2024 Evolution

How AI development transformed from "vibe coding" to autonomous agents running 30+ hours. The mental shift from managing implementation details to directing goals.

Eli
Eli
Systems Architect, NH/VT

I've been building software since college (C++, Java circa 2000), but 2024 changed everything. This is the story of how AI development evolved from copy-paste chaos to autonomous agents that genuinely understand projects and work for days without supervision.

The Evolution Timeline

Early 2024: "Vibe Coding"

  • Describe what you want in natural language
  • Get code back
  • Hope it works
  • Lots of iteration and copy-paste

Mid 2024: Prompt Engineering

  • Craft perfect prompts with examples
  • Use templates and patterns
  • Focus on getting the prompt "right"
  • Still mostly one-shot attempts

Late 2024: Context Engineering

  • Create PLANNING.md, TASK.md files
  • Break down work into explicit steps
  • Feed structured context to AI
  • More reliable but significant overhead

October 2025: Agentic Development

  • AI agents that actually understand projects
  • Multi-step autonomous work (30+ hours)
  • Checkpoints and state management
  • Iterative refinement built-in
  • Context persists across sessions

Before vs After: Managing Everything vs Directing Goals

Before: You Were the Project Manager

The old workflow looked like this:

You: Write PLANNING.md (explain architecture)
You: Write TASK.md (break into steps)
You: Feed to AI assistant
You: Copy code back
You: Test
You: Write new TASK.md for fixes
You: Repeat

You were the project manager, orchestrator, and QA. Exhausting.

Now: Agents Manage Themselves

The new workflow with Claude Code + Agents SDK:

You: "Build a resale certificate agent that queries Buildium,
     validates data, generates PDFs, and emails results.
     It should run autonomously with checkpoints."

Agent: - Explores your codebase
       - Designs architecture
       - Implements incrementally
       - Tests itself
       - Fixes errors
       - Creates checkpoints
       - Runs for 30+ hours if needed
       - Reports back with working solution

The agent is now the project manager, orchestrator, and QA.

This isn't hyperbole. Claude Sonnet 4.5 (released Sept 2025) can genuinely work autonomously for 30+ hours with checkpoint management. This changes everything.

The Four Key Shifts

1. From Files to Conversations

Before

  • ✗ PLANNING.md
  • ✗ TASK.md
  • ✗ ARCHITECTURE.md
  • ✗ Lots of file management

Now

  • ✓ Conversational direction
  • ✓ Agent maintains context
  • ✓ Built-in memory/state
  • ✓ Files created as needed

2. From Steps to Goals

Before (Micromanagement):

TASK.md:
[ ] Create database schema
[ ] Write API endpoint
[ ] Add error handling
[ ] Write tests

Now (Goal-Oriented):

"Build a data validation system that ensures HOA fees
are within 20% of association average. It should flag
outliers and log all decisions."

Agent figures out the steps.

3. From One-Shot to Iterative

The most powerful shift: agents now test themselves, see errors, and fix them automatically. No more copying error messages back and forth.

4. From Stateless to Stateful

Before, every prompt started fresh. Now, agents maintain context across sessions, resume from checkpoints, and remember previous work. This is the foundation that makes 30+ hour runs possible.

The Mental Shift: From Compiler to Product Owner

Before: You Were the Compiler

Your role:

  • Translate business logic → technical steps
  • Break down into implementable chunks
  • Manage state between interactions
  • Remember context manually
  • Orchestrate the entire process

Result: You were exhausted.

Now: You're the Product Owner

Your role:

  • Define the problem
  • Explain business context
  • Validate the solution
  • Approve before production
  • Measure outcomes

Result: Much less exhausting.

Real Example: The Difference in Practice

Old Way: Context Engineering (Late 2024)

PLANNING.md

# Resale Certificate Generator

## Architecture
- Query Buildium API for property data
- Validate data completeness
- Fill PDF template
- Store in R2
- Email to title company

## Tasks
1. Set up Buildium API client
2. Create data validation module
3. Implement PDF generation
4. Configure email service
5. Add error handling
6. Write tests

TASK.md

# Current Task: Buildium API Client

## Steps
- [ ] Install fetch library
- [ ] Create API wrapper class
- [ ] Add authentication
- [ ] Implement getProperty method
- [ ] Add error handling
- [ ] Write unit tests

Then feed these files to your AI assistant, get code, test, update TASK.md, repeat. Tedious.

New Way: Agentic Development (October 2025)

Your request:

I need to automate resale certificates for my property management company.

CONTEXT:
- I use Buildium for property data (API docs: [URL])
- Resale certificates have specific required fields (list)
- Title companies need PDFs emailed within 24 hours
- HOA fees must be validated against association averages

REQUIREMENTS:
- Query Buildium when I provide property address
- Validate all data (flag if fees seem wrong)
- Generate PDF using template (I'll provide)
- Email to title company
- Log all decisions for audit

SUCCESS CRITERIA:
- Generate 3 test certificates matching manual process
- Flag test case with incorrect HOA fee
- Run end-to-end in under 2 minutes
- All data validated before PDF creation

CONSTRAINTS:
- Don't email test certificates (mock email during development)
- Don't modify Buildium data (read-only)
- Must work with my existing Obsidian MCP setup

Build this incrementally, test as you go, and use checkpoints
so I can resume if interrupted.

That's it. The AI agent then:

  1. Figures out the architecture
  2. Breaks into tasks internally
  3. Implements incrementally
  4. Tests each piece
  5. Fixes errors it encounters
  6. Shows you progress
  7. Creates checkpoints
  8. Delivers working solution

Best Practices for October 2025

1. Goal-Oriented Prompts

Good ✓

"Build an agent that monitors competitor prices daily, flags changes >10%, and updates my dashboard."

Bad ✗

"First create a database schema with these columns... Then write a function to query competitor API..."

2. Business Context First

Don't just describe the technical requirement—explain why it matters:

Good Example:

"I need to validate HOA fees because mistakes in resale certificates can delay closings and cost us customers. Fees should be within 20% of association average."

3. Trust + Verify

Let the agent build the solution its way, then validate business logic:

  • ✓ Let agent build solution
  • ✓ Run the tests/validation
  • ✓ Check business logic correctness
  • ✓ Approve or redirect
  • ✗ Don't specify every function name
  • ✗ Don't dictate file structure
  • ✗ Don't micro-manage approach

4. Use Checkpoints

For complex integrations, request checkpoints every 30-60 minutes. This lets you review progress and resume if anything breaks.

Moving Forward: What This Means for You

You've Moved From:

  • ✗ Writing detailed specs (PLANNING.md)
  • ✗ Breaking into tasks (TASK.md)
  • ✗ Managing execution
  • ✗ Maintaining context
  • ✗ Orchestrating everything

To:

  • ✓ Describing problems
  • ✓ Providing business context
  • ✓ Validating solutions
  • ✓ Approving deployment
  • ✓ Measuring outcomes

This is the right evolution for your role.

You're the business expert who understands:

  • HOA regulations
  • Resale certificate requirements
  • E-commerce logistics
  • Property management workflows

The agent is the implementation expert who:

  • Translates your requirements to code
  • Handles technical details
  • Tests and iterates
  • Maintains state
  • Runs until complete

Your advantage: You know what needs to be built.

Agent's advantage: It knows how to build it.

Together: You build production tools in days instead of weeks.

Key Takeaways

  • 🎯 Agentic development is fundamentally different from prompt engineering—it's about directing goals, not managing steps.
  • ⏱️ Agents can now run 30+ hours autonomously with checkpoint management (Claude Sonnet 4.5, Sept 2025).
  • 📋 Stop creating PLANNING.md and TASK.md files—describe your problem conversationally with business context.
  • 🔄 Your role shifted from compiler to product owner—you define what, agents figure out how.
  • Trust + verify—let agents build their way, then validate business logic and approve deployment.
Eli

About Eli

Systems Architect based in NH/VT. I design systems, AI agents build them. Background in systems administration and 25+ years of hardware/troubleshooting experience. Currently building production AI solutions for property management and e-commerce.

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