Add CONTEXT.md for AI agent consumption

CONTEXT.md

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+# tkn CLI Agent Context
+
+This file describes `tkn` conventions, output formats, and behavioral notes
+for automated and agent-driven workflows. For contributing to tkn itself,
+see `AGENTS.md`.
+
+---
+
+## Resource Types
+
+Tekton has two layers:
+
+- Definitions (`pipeline`, `task`): reusable templates
+- Runs (`pipelinerun`, `taskrun`): execution instances
+
+Supported verbs per resource type:
+
+| Resource | Verbs |
+|---|---|
+| `pipeline`, `task` | `list`, `describe`, `start`, `logs`, `delete`, `export` |
+| `pipelinerun`, `taskrun` | `list`, `describe`, `logs`, `cancel`, `delete`, `export` |
+
+---
+
+## Common Workflows
+
+List pipeline runs:
+
+```bash
+tkn pipelinerun list --output json
+```
+
+Inspect run status:
+
+```bash
+tkn pipelinerun describe <run-name> --output json
+tkn taskrun describe <run-name> --output json
+```
+
+Get logs for the most recent run:
+
+```bash
+tkn pipelinerun logs --last
+tkn taskrun logs --last
+```
+
+Start a pipeline non-interactively:
+
+```bash
+tkn pipeline start <pipeline-name> \
+  --param <key>=<value> \
+  --workspace name=<ws-name>,claimName=<pvc-name> \
+  --use-param-defaults \
+  --skip-optional-workspace \
+  --showlog
+```
+
+Re-run the most recent pipeline run:
+
+```bash
+tkn pipeline start <pipeline-name> --last --use-param-defaults
+```
+
+Delete a run:
+
+```bash
+tkn pipelinerun delete <run-name> --force
+tkn taskrun delete <run-name> --force
+```
+
+---
+
+## Output Formats
+
+| Command | JSON output | Notes |
+|---|---|---|
+| `list` | Yes | Supported on all resources |
+| `describe` | Yes | Supported on all resources |
+| `logs` | No | Plain text to stdout only |
+| `start` | No | Prints run name to stdout on success |
+| `delete` | No | Requires `--force` to skip confirmation |
+| `export` | No | Outputs YAML (Kubernetes manifest) |
+
+`--output yaml` is available wherever `--output json` is supported.
+
+---
+
+## Non-Interactive Usage
+
+`pipeline start` and `task start` prompt for missing parameters and workspaces
+by default. In non-TTY environments, this blocks execution.
+
+For non-interactive use, pass:
+
+```bash
+tkn pipeline start <pipeline-name> \
+  --param <key>=<value> \
+  --use-param-defaults \
+  --skip-optional-workspace
+```
+
+`--use-param-defaults` applies schema defaults for unspecified parameters. If
+a required parameter has no default and is not passed via `--param`, the
+command prompts regardless.
+
+---
+
+## Exit Codes
+
+`tkn pipelinerun logs` defines the following exit codes:
+
+| Code | Meaning |
+|---|---|
+| 0 | PipelineRun succeeded |
+| 1 | PipelineRun failed |
+| 2 | No status conditions available |
+
+Exit code behavior is only documented for `pipelinerun logs`. Other commands
+do not define stable exit code semantics.
+
+---
+
+## Behavioral Notes
+
+**`taskrun logs` exit code does not reflect run outcome.** A failed TaskRun
+exits 0. To check TaskRun outcome, inspect `.status.conditions[0].status`:
+
+```bash
+tkn taskrun describe <run-name> --output json
+```
+
+**`delete` requires `--force` on all resources.** Without `-f`, the command
+prompts for confirmation.
+
+**`--last` targets the most recent run by creation time.** In concurrent
+environments, capture the run name from `pipeline start` stdout and pass it
+explicitly to subsequent commands.
+
+**`logs` does not support structured output.** Log content goes to stdout;
+errors go to stderr.
+
+**`export` outputs YAML only.** Use `describe --output json` for structured
+status inspection.
+
+---
+
+## Common Flags
+
+| Flag | Commands | Purpose |
+|---|---|---|
+| `--output json` | `list`, `describe` | Machine-readable output |
+| `--last` | `logs`, `start`, `describe` | Target most recent run |
+| `--use-param-defaults` | `start` | Use schema defaults for unspecified params |
+| `--skip-optional-workspace` | `start` | Skip prompts for optional workspaces |
+| `--force`, `-f` | `delete` | Skip confirmation prompt |
+| `--showlog` | `start` | Stream logs after starting |
+| `--namespace`, `-n` | all | Override kubeconfig namespace |
+| `--param`, `-p` | `start` | Pass parameter as `<key>=<value>` |
+| `--workspace`, `-w` | `start` | Pass workspace binding |