Focus

Blast radius you can defend — evidence-only, before you merge.

When a senior asks why on an AI-assisted PR, “the model wrote it” isn’t an answer.
Focus shows what else that change touches — with evidence you can point at in review.

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Who · What · When · Where · Why · How

Who	Juniors shipping AI-assisted PRs, and seniors who have to review them — anyone who must defend a change
What	An evidence-only blast-radius HUD: import graph → Mermaid map + Danger Zones. No LLM inventing edges
When	Right before you push, and on every PR — the moment someone asks “what else breaks?” or “why this?”
Where	A: GitHub PR comment (full HUD). C: inline in the diff — IDE CodeLens + HUD panel now; GitHub file annotations next. Not committed .md files
Why	AI made teams faster at generating code and slower at shared understanding. The feedback loop breaks when the answer is silence
How	Parse the repo → dependency graph → reverse-BFS from the diff → quiet unless it matters. Same FocusHUD everywhere (--format json for the IDE)

Not another AI PR summary. Not a hop inventory that cries wolf on every file.

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Try in 60 seconds

pip install "focus-hud>=0.3.1"
# or: uv tool install focus-hud

focus trace path/to/shared_module.py --out focus-hud.md
# open focus-hud.md → Markdown preview for Mermaid

focus audit --local --out focus-hud.md   # local preview only (gitignored — not committed)
focus audit --local --format json        # machine-readable HUD (IDE / tools)

focus-hud.md is a scratch file for local Mermaid preview. Focus does not ask you to commit HUD output — reviewers get A (PR comment) and C (inline in the diff).

Demo fixture (no app required):

git clone https://github.com/j0viane/focus.git && cd focus
uv sync
uv run focus trace tests/fixtures/glass_box/auth_utils.py \
  --root tests/fixtures/glass_box --out focus-hud.md

Gallery + walkthrough: docs/DEMO.md · docs/assets/

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Where Focus shows up

Surface	When	What you get
A — PR comment	Every PR (GitHub Action)	Full architecture HUD — summary, Mermaid, Danger Zones. Updates in place on new pushes
C — IDE diff	Before you push (Cursor / VS Code)	CodeLens on changed + blast-radius files; click for HUD panel
C — GitHub diff	PR review (planned)	Inline pins on Files changed — companion to the PR comment
B — git	—	Not supported — no committed focus-hud.md

Same evidence everywhere: parse → graph → FocusHUD → renderer (markdown comment, webview, CodeLens, future GitHub annotations).

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In Cursor / VS Code (diff-first · surface C)

CodeLens on changed symbols + per-hunk explainers + click for the full HUD panel — blast radius in the diff you're editing.

What it looks like on a changed function (virtual UI — nothing written to git):

🎯 Focus · _extract_definitions · 🔴 CRITICAL · 22 downstream
   Part of a CRITICAL blast radius — 22 downstream files may be affected.

    def _extract_definitions(tree: ast.AST) -> list[Definition]:
        definitions: list[Definition] = []
        for node in ast.walk(tree):
            if isinstance(node, (ast.FunctionDef, ast.AsyncFunctionDef)):
                ℹ️ Records this as a function in the AST (Abstract Syntax Tree).
                definitions.append(
                    Definition(
                        name=node.name,
                        kind="function",
                        line=node.lineno,
                        docstring=_first_docstring_line(node),
                    )
                )
            elif isinstance(node, ast.ClassDef):
                ℹ️ Records this as a class in the AST (Abstract Syntax Tree).
                definitions.append(
                    Definition(
                        name=node.name,
                        kind="class",
                        line=node.lineno,
                        docstring=_first_docstring_line(node),
                    )
                )

Row	Where	What
🎯 Focus header	Above def / class	Symbol name, risk tier, downstream count + short summary
ℹ️ Detail	Above each edit block	Hunk-local plain English (acronyms expanded for juniors)

pip install "focus-hud>=0.3.1"
./scripts/install-extension.sh   # or: cd extensions/vscode-focus && npm run compile

Then open your repo, set focus.path if needed, and run Focus: Audit Local Changes. Details: extensions/vscode-focus/README.md.

Moment	Command	You get
AI rewrote a shared function	focus audit --local or Focus: Audit Local Changes	C — blast radius in your working diff
Big PR in your queue	Focus Action comment	A — diagram + Danger Zones on the PR
Inherited a module	focus trace path/to/file.py	Downstream map for one file

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GitHub Action (surface A · any repo)

Copy examples/focus-action.yml → .github/workflows/focus.yml.
On every PR open/sync, Focus posts (and updates) a HUD comment — not a file in the commit.

Details: docs/ACTION.md. Permissions: contents: read + pull-requests: write only (docs/PRIVACY.md).

Phase 5: inline annotations on the PR diff (C on GitHub) — see docs/ROADMAP.md.

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Getting started (from this repo)

git clone https://github.com/j0viane/focus.git
cd focus
uv sync
uv run focus scan .
uv run focus trace src/focus/models.py --out focus-hud.md
uv run focus audit --local

Unchanged files reuse .focus-cache/ (gitignored). Pass --no-cache to force a full re-parse.

Optional: copy .focus.toml.example → .focus.toml to tune fan_out_threshold (default 3).

Requirements: Python 3.12+. Install: pip install focus-hud (CLI: focus). Publish notes: docs/PUBLISH.md.

uv run pytest

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Why "Focus"?

The name comes from Horizon Zero Dawn. Aloy navigates an inherited world with her Focus — an AR device that reveals weak points and danger ahead. A legacy codebase is the same kind of world. This Focus scans it so you change it with intel, not blind faith.

Horizon Zero Dawn and Aloy belong to Guerrilla Games — no affiliation, just admiration.

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Architecture

flowchart TB
    subgraph scan [Focus Scan]
        TS[AST Index] --> G[Dependency Graph]
        G --> SURF[Surface Detector]
    end

    subgraph preflight [Blast Radius Engine]
        DIFF[Git Diff / Symbol Target] --> SEED[Changed Symbols]
        SEED --> BFS[Reverse BFS]
        BFS --> DZ[Danger Zone Scorer]
    end

    subgraph hud [Focus HUD]
        ES[Executive Summary]
        MAP[Mermaid Map]
        BR[Blast Radius Report]
    end

    scan --> preflight
    preflight --> hud
    hud --> OUT["A: PR comment · C: IDE / GitHub diff"]

Loading

Layer	Technology
CLI	Python 3.12+ / Typer (--format markdown|json)
AST	Python ast + Tree-sitter (JS/TS)
Graph	NetworkX
Diagrams	Mermaid (GitHub + IDE webview)
CI	Opt-in GitHub Action — PR comment (A); inline diff (C) planned
IDE	VS Code / Cursor — CodeLens + HUD panel (C)

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Commands

Command	Purpose
focus scan [path]	Index the repo (Python + JS/TS)
focus trace [file]	HUD for one file (--format json for tools)
focus audit --local	Working tree vs main
focus audit --base <sha>	PR / branch range
focus version	Installed version

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Roadmap

Phase 3 complete. Phase 4 in progress (IDE C). Phase 5 next (GitHub diff C + A comment). See docs/ROADMAP.md.

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Ethics & privacy

• Evidence-based — no LLM inventing edges
• Privacy-by-design — respects .gitignore; no source to model APIs
• No surveillance — structure, not developer identity
• Opt-in Action — minimum token scope

Doc	Contents
docs/DEMO.md	Walkthrough + gallery
docs/LAUNCH.md	Product Hunt / Show HN drafts
docs/ACTION.md	Action install
docs/HUD.md	HUD schema + JSON contract
docs/ETHICS.md	Responsible use
docs/PRIVACY.md	Data boundaries

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License

MIT © 2026 Joviane Bellegarde.

Author

Joviane Bellegarde. Feedback welcome via Issues.