<SpecSection title="What this feature specifies" id="what-this-feature-specifies">
How the corelib observes **terminal size changes** and notifies UI code: `Platform.Terminal.QuerySize`, `PollResize` → `Channel<ConsoleMessage>`, and same-fiber `OnResize` event hubs. No new runtime builtins—only existing environment, ioctl externs, and fiber/channel primitives.
</SpecSection>

<SpecSection title="Contract statement" id="contract-statement">
- `Console.ConsoleSize` uses **character cells** (`columns`, `rows` as `i32`).
- `QuerySize` **must** try platform `Winsize` (Linux, macOS, Windows) then fall back to `COLUMNS` / `LINES` parsing.
- `PollResize` **must** `Send` `ConsoleMessage::Resize(now)` only when dimensions change.
- `SubscribeOnResize` **must** invoke the handler synchronously once with the current size after subscription.
- Resize delivery **must not** use a separate OS-thread callback API in v1.
</SpecSection>

<SpecSection title="Implementation anchors" id="implementation-anchors">
- `compiler/corelib/packages/console/src/Platform/Terminal.bd`
- `compiler/corelib/packages/console/src/Console.bd`
- `compiler/corelib/packages/console/src/Console/ConsoleMessage.bd`
- Tests: `ConsoleMessageChannelTests.bd`
</SpecSection>

## Decisions
<!-- spec:generate:adr-index -->
No open decisions. Closed choices are normative ADRs under **`adr/`** (`D-CORE-TERM-0050` … `D-CORE-TERM-0052`); use the reader **ADRs** tab for expandable detail.
<!-- /spec:generate:adr-index -->
## Articles
<!-- spec:generate:article-index -->
- [Contracts and edge cases](./articles/contracts-and-edge-cases/)
- [Design model](./articles/design-model/)
- [Examples](./articles/examples/)
- [Flow and algorithm](./articles/flow-and-algorithm/)
- [Verification and traceability](./articles/verification-and-traceability/)
<!-- /spec:generate:article-index -->

## Context

Resize notifications must integrate with fiber concurrency without OS-thread callbacks.

## Decision

| Rule | Detail |
| --- | --- |
| Cross-fiber | `PollResize` → `` `Channel<ConsoleMessage>` `` |
| Same-fiber | `OnResize` event hub |

## Consequences

No separate OS-thread callback API in v1.

## Verification anchors

`ConsoleMessageChannelTests.bd`.

## Context

Not all hosts expose Winsize ioctl; env vars are a portable fallback.

## Decision

| Rule | Detail |
| --- | --- |
| Order | Winsize ioctl then `COLUMNS`/`LINES` |
| Parse | Discrete table, not full integer grammar in v1 |

## Consequences

Odd env values may clamp or ignore per contracts article.

## Verification anchors

`Platform/Terminal.bd` tests.

## Context

UI loops should not crash when consumers drop resize messages.

## Decision

| Rule | Detail |
| --- | --- |
| EVT-002 | Failed `Send` on resize is **silent** in v1 |
| Future | May gain diagnostics in a later ADR |

## Consequences

Poll loops continue after dropped resize notifications.

## Verification anchors

`ConsoleMessageChannelTests.bd`; EVT-002 traceability.

## Purpose

Document **contracts and edge cases** for the **Console Terminal Events** feature: role-specific normative detail beyond the feature hub.

## Canonical references

- Feature hub: [Console Terminal Events](/platform-spec/core-library/terminal-and-console/console-terminal-events/)
- Sibling articles in this bundle (design model, contracts, flow, examples, verification)

## Detailed behavior

### Normative requirements

| ID | Requirement |
| --- | --- |
| **EVT-001** | `PollResize` **must** compare against `lastSize` and only send on change. |
| **EVT-002** | Failed `Channel.Send` **must** be ignored silently in v1 poll loop (no panic). |
| **EVT-003** | `SubscribeOnResize` **must** set `hub.lastSize` and raise `OnResize` immediately with `QuerySize()`. |
| **EVT-004** | Default size when all probes fail **should** be 80×24 via env fallback. |

### Edge cases

- **Non-TTY stdout**: `QuerySize` may return env defaults; resize events may never fire.
- **Rapid resize**: Coalescing is caller responsibility; each poll may emit at most one message.
- **Closed channel**: `Send` errors are dropped per EVT-002.

## Verification

See the verification and traceability article in this bundle and `compiler/corelib/beskid_corelib/tests/corelib_tests/src/console/`.

## Related topics

- Parent [feature hub](/platform-spec/core-library/terminal-and-console/console-terminal-events/) and [Terminal and console area](/platform-spec/core-library/terminal-and-console/)

## Purpose

Document **design model** for the **Console Terminal Events** feature: role-specific normative detail beyond the feature hub.

## Canonical references

- Feature hub: [Console Terminal Events](/platform-spec/core-library/terminal-and-console/console-terminal-events/)
- Sibling articles in this bundle (design model, contracts, flow, examples, verification)

## Detailed behavior

### `ConsoleMessage`

| Variant | Payload | Use |
| --- | --- | --- |
| `Resize(ConsoleSize)` | columns/rows | Terminal geometry changed |
| (tick-related) | — | Integrated with `Console.RunTick` polling |

Messages flow on an **unbounded** `Channel<ConsoleMessage>` created by `Console.MessagesChannel()` unless callers supply their own channel.

### `OnResize` hub

Same-fiber `event OnResize(ConsoleSize)` with cached `lastSize`. Distinct from `Concurrency.Hub` (channel multiplexing). Use when resize handlers must run on the UI fiber without cross-fiber `Send`.

### Size probing stack

```mermaid
flowchart TD
  winsize[Platform Winsize ioctl]
  env[COLUMNS / LINES env]
  query[Terminal.QuerySize]
  winsize --> query
  env --> query
```

ANSI screen modes are unrelated to size events; see [ANSI escape model](/platform-spec/core-library/terminal-and-console/ansi-escape-model/).

## Verification

See the verification and traceability article in this bundle and `compiler/corelib/beskid_corelib/tests/corelib_tests/src/console/`.

## Related topics

- Parent [feature hub](/platform-spec/core-library/terminal-and-console/console-terminal-events/) and [Terminal and console area](/platform-spec/core-library/terminal-and-console/)

## Purpose

Document **examples** for the **Console Terminal Events** feature: role-specific normative detail beyond the feature hub.

## Canonical references

- Feature hub: [Console Terminal Events](/platform-spec/core-library/terminal-and-console/console-terminal-events/)
- Sibling articles in this bundle (design model, contracts, flow, examples, verification)

## Detailed behavior

### Channel loop

```beskid
Channel<ConsoleMessage> messages = Console.MessagesChannel();
ConsoleSize last = Console.QuerySize();
// spawn fiber: loop { Console.RunTick(messages, last); Receive and handle Resize }
```

### Same-fiber event hub

```beskid
OnResize hub = OnResize { lastSize: Console.QuerySize(), OnResize: ... };
Console.SubscribeOnResize(hub, handler);
Platform.Terminal.PollResizeHub(hub);
```

After `Resize`, call [Console controls](/platform-spec/core-library/terminal-and-console/console-controls/) `Frame.Render` with the new `ConsoleSize`.

## Verification

See the verification and traceability article in this bundle and `compiler/corelib/beskid_corelib/tests/corelib_tests/src/console/`.

## Related topics

- Parent [feature hub](/platform-spec/core-library/terminal-and-console/console-terminal-events/) and [Terminal and console area](/platform-spec/core-library/terminal-and-console/)

## Purpose

Document **flow and algorithm** for the **Console Terminal Events** feature: role-specific normative detail beyond the feature hub.

## Canonical references

- Feature hub: [Console Terminal Events](/platform-spec/core-library/terminal-and-console/console-terminal-events/)
- Sibling articles in this bundle (design model, contracts, flow, examples, verification)

## Detailed behavior

### `PollResize` algorithm

1. `now ← QuerySize()` (platform winsize chain → env fallback)
2. If `now.columns != lastSize.columns` OR `now.rows != lastSize.rows`:
   - `lastSize ← now`
   - `messages.Send(ConsoleMessage::Resize(now))` (ignore send errors)
3. Return

### `PollResizeHub` (same fiber)

Compare `hub.lastSize` to `QuerySize()`; on change update cache and invoke `hub.OnResize(now)` synchronously.

### `RunTick`

Delegates to `Platform.Terminal.PollResize` then optional tick messages for controls—pairs with [Console controls](/platform-spec/core-library/terminal-and-console/console-controls/flow-and-algorithm/).

## Verification

See the verification and traceability article in this bundle and `compiler/corelib/beskid_corelib/tests/corelib_tests/src/console/`.

## Related topics

- Parent [feature hub](/platform-spec/core-library/terminal-and-console/console-terminal-events/) and [Terminal and console area](/platform-spec/core-library/terminal-and-console/)

## Purpose

Document **verification and traceability** for the **Console Terminal Events** feature: role-specific normative detail beyond the feature hub.

## Canonical references

- Feature hub: [Console Terminal Events](/platform-spec/core-library/terminal-and-console/console-terminal-events/)
- Sibling articles in this bundle (design model, contracts, flow, examples, verification)

## Detailed behavior

| Artifact | Role |
| --- | --- |
| `Platform/Terminal.bd` | `QuerySize`, `PollResize`, env fallback |
| `Console.bd` | `RunTick`, `SubscribeOnResize`, `MessagesChannel` |
| `ConsoleMessageChannelTests.bd` | Channel resize delivery |

Platform stubs: `Platform/Linux.bd`, `MacOS.bd`, `Windows.bd` winsize externs.

## Verification

See the verification and traceability article in this bundle and `compiler/corelib/beskid_corelib/tests/corelib_tests/src/console/`.

## Related topics

- Parent [feature hub](/platform-spec/core-library/terminal-and-console/console-terminal-events/) and [Terminal and console area](/platform-spec/core-library/terminal-and-console/)