NexusScan — Development Report

Project: NexusScan v1.0.0 Type: CLI Tool (Python) Profile: Casual Source: github.com/loskylp/NexusScan Session transcript: NexusScan-TRANSCRIPT.md Retrospective: NexusScan-RETROSPECTIVE.md Date: 2026-03-17

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Overview

NexusScan is a command-line utility that recursively scans a directory and reports file type distribution: counts and total sizes per extension, rendered as an ASCII table in the terminal. It was developed as the first real-world test of the Nexus SDLC framework, exercising the full agent swarm lifecycle from requirements through go-live.

The project was chosen deliberately for its simplicity — a casual-profile CLI tool with no network, no auth, and no persistence — to validate the framework’s ability to manage scope, apply appropriate ceremony, and ship a correct, tested artifact without over-engineering.

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Initial Prompt

“Create a CLI tool that scans a directory and counts files by extension.”

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Lifecycle Summary

The development ran through all six Nexus SDLC gates. Every gate required explicit human (Nexus) approval before the swarm could proceed.

Gate	Status	Notes
Requirements	Approved	3 iterations to incorporate expanded brief and execution timer
Architecture	Approved	Walker → Classifier → Renderer pipeline; language deferred to Builder
Plan	Approved	5 tasks; TASK-001 walking skeleton as first deliverable
Execution	Complete	Mid-cycle scope addition of REQ-010 and REQ-011 handled cleanly
Demo Sign-off	Approved	All scenarios validated
Go-Live	Approved	v1.0.0 released

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Requirements

The final requirements set evolved across three iterations. The initial prompt produced five requirements; two rounds of refinement from the expanded brief added symlink handling, execution timer, size column, and directory exclusion.

ID	Requirement	Origin
REQ-001	Scan target directory, default to cwd	Initial
REQ-002	Classify by normalized (lowercase) extension; files with no extension → (no extension)	Initial
REQ-003	ASCII table with box-drawing borders, sorted by frequency descending, with total	Refined
REQ-004	Recursive traversal only	Initial
REQ-005	Silently ignore broken symbolic links	Expanded brief
REQ-006	Invalid path → descriptive error on stderr + exit code 1	Initial
REQ-007	Non-interactive; all input via arguments	Expanded brief
REQ-008	Display wall-clock execution time after scan	User addition
REQ-010	Total size per extension, human-readable (B / KB / MB / GB)	Mid-cycle user request
REQ-011	--exclude <name> flag, repeatable (e.g. --exclude node_modules --exclude .git)	Mid-cycle user request
NFR-001	Full pipeline must scan 10,000 files in under 1 second	Architecture gate

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Architecture

System metaphor: A tally clerk walking a filing cabinet — counting documents by type and printing a summary receipt.

The tool is a single-pass, stateless three-stage pipeline:

Walker  →  Classifier  →  Renderer

Stage	Responsibility
Walker	Recursive traversal via os.walk(); prunes excluded directories; skips broken symlinks
Classifier	Extracts and normalizes extension; accumulates count and byte total per group
Renderer	Sorts groups by count descending; draws ASCII table; appends execution time line

Key constraints applied:

• Reads file metadata only — never opens file contents
• No external dependencies — Python standard library only
• Language choice deferred to Builder with the constraint that NFR-001 must be demonstrably met

The Builder chose Python 3. os.walk() + collections.defaultdict is I/O-bound rather than CPU-bound; the performance bottleneck is filesystem access, not the Python runtime. This proved sufficient: 0.08s for 10,000 files.

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Execution Plan

The planner produced five tasks. TASK-001 (walking skeleton) was designated as the first meaningful deliverable — the tool would be fully usable after that task alone.

Task	Description	Covers	Depends On
TASK-001	Walking skeleton: Walker + Classifier + Renderer	REQ-001–004, 007	—
TASK-002	Broken symlink handling	REQ-005	TASK-001
TASK-003	Error handling for invalid paths	REQ-006	TASK-001
TASK-004	Execution timer	REQ-008	TASK-001
TASK-005	Performance benchmark	NFR-001	TASK-001, 004

After TASK-001 passed, the user requested two new features (size column and --exclude flag). The swarm paused execution, ran the requirements gate again, and added TASK-006 to the front of the queue before continuing.

Task	Description	Covers	Inserted
TASK-006	Size column + --exclude flag (amends core pipeline)	REQ-003 rev., REQ-010, REQ-011	Mid-cycle

TASK-006 also incorporated TASK-002, 003, and 004 in the same build pass. TASK-005 ran last to confirm the size stat calls did not break the performance budget.

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Implementation

Source: src/nexusscan.py Language: Python 3.6+ Dependencies: Standard library only (argparse, os, sys, time, collections) Lines of code: 202

Core functions

walk_directory(path, exclude_dirs=None) Generator yielding regular file paths. Prunes excluded directory names from os.walk() in-place to avoid descending into them. Silently skips broken symlinks by checking os.path.islink and os.path.exists.

classify_extensions(file_paths) Iterates the generator, lowercases each extension, groups into a defaultdict accumulating [count, total_bytes]. Files with no extension are keyed as (no extension). OSError on stat is handled gracefully (size defaults to 0).

render_table(extension_data) Sorts groups by count descending (alphabetically for ties), calculates dynamic column widths, and renders an ASCII box-drawing table with header, one row per extension, and a total row. Columns: Extension, Count, Size.

main() Validates the target path, wraps the pipeline in a time.time() measurement, and prints Scan completed in N.NNs after the table. Exits with code 1 on path errors.

Sample output

+----------------+-------+--------+
| Extension      | Count | Size   |
+----------------+-------+--------+
| .md            |    50 | 48.2KB |
| .sample        |    14 |  8.1KB |
| (no extension) |    13 |  2.4KB |
| .py            |     1 |  4.9KB |
| .sh            |     6 |  9.3KB |
+----------------+-------+--------+
| Total          |    84 | 72.9KB |
+----------------+-------+--------+
Scan completed in 0.01s

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Verification

Total acceptance tests: 47 across 6 test scripts Final result: 47/47 passing, 0 retries across all tasks

Test File	Task	Tests	Result
test_task001.sh	Walking skeleton	13	PASS
test_task006.sh	Size column + --exclude	13	PASS
test_task002.sh	Broken symlink handling	5	PASS
test_task003.sh	Error handling	6	PASS
test_task004.sh	Execution timer	5	PASS
test_task005.sh	Performance benchmark	5	PASS — 0.08s for 10,000 files

Each test script creates isolated temporary directories, verifies stdout/stderr content and exit codes, and cleans up after itself.

Performance result: 0.08s for 10,000 files — 12× under the 1-second budget (NFR-001).

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Agents Active

The Methodologist selected a lean swarm for a Casual-profile project, skipping the Designer, Scaffolder, Sentinel, DevOps, and Scribe agents as unnecessary ceremony for a simple CLI tool.

Agent	Role	Contributed
Methodologist	Set profile, selected active agents, configured gates	Methodology Manifest
Orchestrator	Managed hand-offs, gates, state, mid-cycle scope change	Project state, briefings, routing
Analyst	Extracted and refined requirements from user input	Requirements table (3 iterations)
Auditor	Reviewed requirements for completeness and consistency	Audit report
Architect	Designed pipeline, selected Walker/Classifier/Renderer model	Architecture overview
Planner	Decomposed architecture into tasks, set dependencies	Task plan
Builder	Implemented all six tasks in Python	nexusscan.py, 6 acceptance test scripts
Verifier	Ran acceptance tests, reported pass/fail per task	Verification reports

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Framework Observations

This run exposed several real behaviors of the Nexus SDLC framework in practice.

What worked well:

• The requirements gate caught missing details early. The two-iteration refinement (expanded brief → user additions) produced a well-specified requirements set before any code was written.
• Mid-cycle scope addition (REQ-010, REQ-011) was handled without rework. The Orchestrator paused execution, inserted TASK-006, and resumed cleanly.
• The planning constraint that TASK-001 must produce a fully usable tool gave the project a natural early checkpoint — the user could have stopped there with working software.
• Zero test failures and zero retries across the full build is a meaningful signal for a Casual-profile project. No iteration loop was needed.

Friction points observed:

• The tool permission prompts for each Bash command interrupted flow at high frequency during the Builder phase. A trust level or session-scoped permission would reduce this.
• A context limit was hit mid-session (between TASK-005 and the verification pass), requiring a manual “continue” to resume. The Orchestrator recovered correctly by re-reading project state, but the interruption was visible.
• Process document templates in resources/ were never filled in — the agents wrote their output directly in the conversation and to the process/ directory. The template files exist but remain empty placeholders in this run.

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Usage

# Scan current directory
python3 src/nexusscan.py

# Scan a specific path
python3 src/nexusscan.py /path/to/directory

# Exclude directories
python3 src/nexusscan.py /path/to/directory --exclude node_modules --exclude .git

# Run all acceptance tests
for t in tests/acceptance/test_task*.sh; do bash "$t"; done

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Outcome

NexusScan v1.0.0 shipped with all 11 requirements satisfied, 47/47 tests passing, and performance 12× under budget. The project was completed in a single session with no task retries and one mid-cycle scope addition absorbed without rework.

As a framework validation, this run confirmed that the Casual profile produces a lean, functional process: the swarm applied enough structure to catch scope creep early and produce traceable decisions, without blocking delivery on ceremony the project didn’t need.