+++
title = "ASCII graph rendering in display.rs"
priority = 5
status = "done"
ticket_type = "feature"
dependencies = ["9c9ebe"]
+++
Add `format_graph` and `print_graph` to `src/display.rs` to render a ticket dependency DAG as an ASCII tree.

## Motivation

The `nbd graph` command needs to convert the `TicketGraph` data structure (from `src/graph.rs`) into a human-readable ASCII representation. Rendering belongs in `display.rs` next to `format_list` and `format_ticket`.

## Output format

The graph is a forest of trees. Each root ticket (no in-graph dependencies) starts at column 0. Its dependents (tickets that depend on it) are indented below it using box-drawing characters.

```
a3f9c2  [todo]        Fix login bug
├── b7d41e  [todo]    Add rate limiting
│   └── c9e823  [in_progress]  Write tests
└── d1f302  [done]    Update docs
e4a781  [todo]        New feature (no deps)
```

**Node format per line:**
```
{prefix}{id}  [{status}]  {title}
```

Where `{prefix}` is built from indentation characters (`│   `, `├── `, `└── `).

**Blocked indicator (optional):** Consider marking tickets that have unresolved (non-done/closed) dependencies with a `[blocked]` tag or `!` prefix so the graph visually distinguishes ready from blocked tickets.

## Signatures

```rust
/// Render the full dependency forest as an ASCII tree string.
pub fn format_graph(graph: &TicketGraph) -> String

/// Print the full dependency forest.
pub fn print_graph(graph: &TicketGraph)

/// Render the subtree rooted at `root_id` as an ASCII tree string.
pub fn format_subtree(graph: &TicketGraph, root_id: &str) -> String

/// Print the subtree rooted at `root_id`.
pub fn print_subtree(graph: &TicketGraph, root_id: &str)
```

## Implementation notes

- Use a recursive helper that tracks a `prefix: String` carrying the accumulated indentation characters.
- For each node's children (its dependents in the graph), iterate:
  - If not the last child: prefix extension is `│   `; connector is `├── `.
  - If the last child:  prefix extension is `    `;  connector is `└── `.
- Cycle guard: track a `visited: HashSet<&str>` across the recursion; if a node ID is already visited, render `{prefix}{connector}{id}  [cycle]` and stop descending.
- Status is shown as the serde string: `todo`, `in_progress`, `done`, `closed`.

## Files touched
- `src/display.rs` — `format_graph`, `print_graph`, `format_subtree`, `print_subtree`

## Tests (unit, in `src/tests.rs`)
- `format_graph` on a single ticket with no deps produces a single line.
- `format_graph` on a two-ticket chain shows the child indented with `└──`.
- `format_graph` with a branching parent shows `├──` for all but the last child and `└──` for the last.
- `format_subtree` only shows the specified root's subtree.
- A cycle in the graph does not cause infinite recursion; the repeated node is labelled `[cycle]`.