# `Journey`
[🔗](https://github.com/shipworthy/journey/blob/main/lib/journey.ex#L1)

This module is the entry point for the Journey library. It provides functions for creating and managing computation graphs, starting and managing executions, and retrieving values from executions.

Here is a quick example of how to use the library, illustrating the basic concepts of defining a graph, starting an execution of the graph, and setting input values and getting computed values.

```elixir
iex> # 1. Define a graph capturing the data and the logic of the application -
iex> #    the nodes, their dependencies, and their computations:
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "horoscope workflow - module doctest",
...>       "v1.0.0",
...>       [
...>         input(:first_name),
...>         input(:birth_day),
...>         input(:birth_month),
...>         compute(
...>           :zodiac_sign,
...>           # Depends on user-supplied data:
...>           [:birth_month, :birth_day],
...>           # Computes itself, once the dependencies are satisfied:
...>           fn %{birth_month: _birth_month, birth_day: _birth_day} ->
...>             {:ok, "Taurus"}
...>           end
...>         ),
...>         compute(
...>           :horoscope,
...>           # Computes itself once :first_name and :zodiac_sign are in place:
...>           [:first_name, :zodiac_sign],
...>           fn %{first_name: name, zodiac_sign: zodiac_sign} ->
...>             {:ok, "🍪s await, #{zodiac_sign} #{name}!"}
...>           end
...>         )
...>       ]
...>     )
iex>
iex> # 2. For every customer visiting your website, start a new execution of the graph:
iex> e = Journey.start(graph)
iex>
iex> # 3. Populate the execution's nodes with the data as provided by the visitor:
iex> e = Journey.set(e, :birth_day, 26)
iex>
iex> # As a side note: if the user leaves and comes back later or if everything crashes,
iex> # you can always reload the execution using its id:
iex> e = Journey.load(e.id)
iex>
iex> # Continuing, as if nothing happened:
iex> e = Journey.set(e, :birth_month, "April")
iex>
iex> # 4. Now that we have :birth_month and :birth_day, :zodiac_sign will compute itself:
iex> {:ok, "Taurus", _revision} = Journey.get(e, :zodiac_sign, wait: :any)
iex> Journey.values(e) |> redact([:execution_id, :last_updated_at])
%{birth_day: 26, birth_month: "April", zodiac_sign: "Taurus", execution_id: "...", last_updated_at: 1234567890}
iex>
iex> # 5. Once we get :first_name, the :horoscope node will compute itself:
iex> e = Journey.set(e, :first_name, "Mario")
iex> {:ok, "🍪s await, Taurus Mario!", 7} = Journey.get(e, :horoscope, wait: :any)
iex>
iex> Journey.values(e) |> redact([:execution_id, :last_updated_at])
%{birth_day: 26, birth_month: "April", first_name: "Mario", horoscope: "🍪s await, Taurus Mario!", zodiac_sign: "Taurus", execution_id: "...", last_updated_at: 1234567890}
iex>
iex> # 6. and we can always list executions.
iex> this_execution = Journey.list_executions(graph_name: "horoscope workflow - module doctest", order_by_execution_fields: [:inserted_at]) |> Enum.reverse() |> hd
iex> e.id == this_execution.id
true
```

## `f_on_save` callbacks

`f_on_save` is an optional callback for observing node value changes. Two
levels are supported, both following the same contract:

- **Graph-wide**: `Journey.new_graph(name, version, nodes, f_on_save: fn ... end)`
  fires for every node value change in the graph (inputs and steady-state nodes).
- **Node-scoped**: each `Journey.Node` function (`input/2`, `compute/4`,
  `mutate/4`, `archive/3`, `historian/3`, `tick_once/4`, `tick_recurring/4`,
  `loop/4`) accepts `f_on_save:` in its options.

When both are defined, the node-scoped callback is dispatched first, but
both run as independent Tasks and may complete in any order.

The callback receives `(execution_id, node_name, result)` and runs
asynchronously in a separate `Task`. Exceptions raised inside the callback
are caught and logged but do not affect the computation's state or
downstream propagation.

`result` is one of:

  - `{:ok, value}` — success (the values table was written). The shape of
    `value` depends on the node type; see each node's docs.
  - `{:error, reason}` — retries exhausted. `reason` is the last `f_compute`
    error, or `"Unexpected value: '<inspected>'"` if `f_compute` returned a
    non-`{:ok, _}`/`{:error, _}` shape (inspected/truncated).
  - `{:error, "timeout"}` — `:abandon_after_seconds` timeout, after retries
    exhausted.

Default: not invoked per-attempt, nor for idempotent no-change re-runs
(when the new value equals the existing value). Exceptions:

  - `loop/4` extends this — also not invoked per-iteration, nor for
    transient iteration errors that get retried.
  - `input/2` only ever fires with `{:ok, value}` (inputs don't have an
    error path).

# `new_graph`

Creates a new computation graph with the given name, version, and node definitions.

## Arities

- `new_graph(nodes)` - Auto-generates name and uses default version "v1.0"
- `new_graph(nodes, opts)` - Auto-generates name with options
- `new_graph(name, nodes)` - Explicit name, default version
- `new_graph(name, nodes, opts)` - Explicit name with options
- `new_graph(name, version, nodes)` - Full specification
- `new_graph(name, version, nodes, opts)` - Full specification with
options

This is the foundational function for defining Journey graphs. It creates a validated
graph structure that can be used to start executions with `start/1`. The graph
defines the data flow, dependencies, and computations for your application workflow.

## Quick Example

```elixir
import Journey.Node
graph = Journey.new_graph(
  "user onboarding",
  "v1.0.0",
  [
    input(:email),
    compute(:welcome_message, [:email], fn %{email: email} ->
      {:ok, "Welcome #{email}!"}
    end)
  ]
)
execution = Journey.start(graph)
```

Use `start/1` to create executions and `set/3` to populate input values.

## Parameters
* `name` - String identifying the graph (e.g., "user registration workflow")
* `version` - String version identifier following semantic versioning (e.g., "v1.0.0")
* `nodes` - List of node definitions created with `Journey.Node` functions (`input/1`, `compute/4`, etc.)
* `opts` - Optional keyword list of options:
  * `:f_on_save` - Graph-wide callback fired for every node value change in
    the graph. Called after any node-scoped `:f_on_save`. See the
    [`f_on_save` callbacks](#module-f_on_save-callbacks) section for the
    shared contract.
  * `:execution_id_prefix` - Custom prefix for execution IDs created from this graph.
    Will be normalized to uppercase. Defaults to "EXEC" if not specified.
    Example: "mygraph" becomes "MYGRAPH1A2B3D4E5G6H7J8L9M"
  * `:singleton` - When `true`, only one non-archived execution can exist for this graph.
    Defaults to `false`.
  * `:keep_latest_completed_computations` - Graph-wide default for computation retention.
    Sets the maximum number of most-recent successful computations to keep per node.
    Older computations beyond this window are automatically deleted after each successful
    completion, with the exception of the 10 oldest computations which are always preserved.
    `nil` (default) means no cleanup. Can be overridden per-node. Example: `keep_latest_completed_computations: 200`

## Returns
* `%Journey.Graph{}` struct representing the validated and registered computation graph

## Errors
* Raises `RuntimeError` if graph validation fails (e.g., circular dependencies, unknown node references)
* Raises `ArgumentError` if parameters have invalid types or empty node list
* Raises `KeywordValidator.Error` if options are invalid

## Key Behaviors
* **Validation** - Automatically validates graph structure for cycles, dependency correctness
* **Registration** - Registers graph in catalog for execution tracking and reloading
* **Immutable** - Graph definition is immutable once created; create new versions for changes
* **Node types** - Supports input, compute, mutate, tick_once, and tick_recurring nodes

## Examples

Basic workflow with input and computation:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "greeting workflow",
...>   "v1.0.0",
...>   [
...>     input(:name),
...>     compute(:greeting, [:name], fn %{name: name} -> {:ok, "Hello, #{name}!"} end)
...>   ]
...> )
iex> graph.name
"greeting workflow"
iex> execution = Journey.start(graph)
iex> execution = Journey.set(execution, :name, "Alice")
iex> {:ok, "Hello, Alice!", 3} = Journey.get(execution, :greeting, wait: :any)
```

Graph with a graph-wide `f_on_save` callback:

```elixir
iex> import Journey.Node
iex> _graph = Journey.new_graph(
...>   "notification workflow",
...>   "v1.0.0",
...>   [
...>     input(:user_id),
...>     compute(:fetch_user, [:user_id], fn %{user_id: id} ->
...>       {:ok, %{id: id, name: "User #{id}"}}
...>     end),
...>     compute(:send_email, [:fetch_user], fn %{fetch_user: user} ->
...>       {:ok, "Email sent to #{user.name}"}
...>     end)
...>   ],
...>   f_on_save: fn _execution_id, node_name, result ->
...>     # This will be called for both :fetch_user and :send_email computations
...>     IO.puts("Node #{node_name} completed with result: #{inspect(result)}")
...>     :ok
...>   end
...> )
```

Complex workflow with conditional dependencies:

```elixir
iex> import Journey.Node
iex> import Journey.Node.Conditions
iex> import Journey.Node.UpstreamDependencies
iex> graph = Journey.new_graph(
...>       "horoscope workflow",
...>       "v1.0.0",
...>       [
...>         input(:first_name),
...>         input(:birth_day),
...>         input(:birth_month),
...>         compute(
...>           :zodiac_sign,
...>           [:birth_month, :birth_day],
...>           fn %{birth_month: _birth_month, birth_day: _birth_day} ->
...>             {:ok, "Taurus"}
...>           end
...>         ),
...>         compute(
...>           :horoscope,
...>           unblocked_when({
...>             :and,
...>             [
...>               {:first_name, &provided?/1},
...>               {:zodiac_sign, &provided?/1}
...>             ]
...>           }),
...>           fn %{first_name: name, zodiac_sign: zodiac_sign} ->
...>             {:ok, "🍪s await, #{zodiac_sign} #{name}!"}
...>           end
...>         )
...>       ]
...>     )
iex> execution = Journey.start(graph)
iex> execution = Journey.set(execution, :birth_day, 15)
iex> execution = Journey.set(execution, :birth_month, "May")
iex> {:ok, "Taurus", _revision} = Journey.get(execution, :zodiac_sign, wait: :any)
iex> execution = Journey.set(execution, :first_name, "Bob")
iex> {:ok, "🍪s await, Taurus Bob!", 7} = Journey.get(execution, :horoscope, wait: :any)
```

Multiple node types in a workflow:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "data processing workflow",
...>   "v2.1.0",
...>   [
...>     input(:raw_data),
...>     compute(:upper_case, [:raw_data], fn %{raw_data: data} ->
...>       {:ok, String.upcase(data)}
...>     end),
...>     compute(:suffix, [:upper_case], fn %{upper_case: data} ->
...>       {:ok, "#{data} omg yay"}
...>     end)
...>   ]
...> )
iex> execution = Journey.start(graph)
iex> execution = Journey.set(execution, :raw_data, "hello world")
iex> {:ok, "HELLO WORLD", 3} = Journey.get(execution, :upper_case, wait: :any)
iex> {:ok, "HELLO WORLD omg yay", 5} = Journey.get(execution, :suffix, wait: :any)
```

Custom execution ID prefix for easier debugging:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "user onboarding",
...>   "v1.0.0",
...>   [
...>     input(:email),
...>     compute(:welcome_message, [:email], fn %{email: email} ->
...>       {:ok, "Welcome #{email}!"}
...>     end)
...>   ],
...>   execution_id_prefix: "onboard"
...> )
iex> execution = Journey.start(graph)
iex> String.starts_with?(execution.id, "ONBOARD")
true
iex> execution = Journey.set(execution, :email, "user@example.com")
iex> {:ok, "Welcome user@example.com!", 3} = Journey.get(execution, :welcome_message, wait: :any)
```

# `new_graph`

# `new_graph`

# `new_graph`

# `archive`

Archives an execution, making it invisible and stopping all background processing.

Archiving permanently (*) freezes an execution by marking it with an archived timestamp.
This removes it from normal visibility and excludes it from all scheduler processing,
while preserving the data for potential future access.

*) an execution can be unarchived by calling `unarchive/1`

## Quick Example

```elixir
archived_at = Journey.archive(execution)
Journey.load(execution)  # Returns nil (hidden)
Journey.load(execution, include_archived: true)  # Can still access
```

Use `unarchive/1` to reverse archiving and `list_executions/1` with `:include_archived` to find archived executions.

## Parameters
* `execution` - A `%Journey.Persistence.Schema.Execution{}` struct or execution ID string

## Returns
* Integer timestamp (Unix epoch seconds) when the execution was archived

## Errors
* Raises if the supplied execution ID does not correspond to an existing execution

## Key Behaviors
* **Scheduler exclusion** - Archived executions are excluded from all background sweeps and processing
* **Hidden by default** - Not returned by `list_executions/1` or `load/2` unless explicitly included
* **Idempotent** - Archiving an already archived execution returns the existing timestamp
* **Reversible** - Use `unarchive/1` to restore normal visibility and processing

## Examples

Basic archiving workflow:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph("archive example", "v1.0.0", [input(:data)])
iex> execution = Journey.start(graph)
iex> execution.archived_at
nil
iex> archived_at = Journey.archive(execution)
iex> is_integer(archived_at)
true
iex> Journey.load(execution)
nil
iex> Journey.load(execution, include_archived: true) != nil
true
```

Idempotent behavior:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph("archive idempotent", "v1.0.0", [input(:data)])
iex> execution = Journey.start(graph)
iex> first_archive = Journey.archive(execution)
iex> second_archive = Journey.archive(execution)
iex> first_archive == second_archive
true
```

# `count_executions`

Returns the count of executions matching the specified criteria.

This function uses database-level counting, and does not load the execution records into memory.

This function provides the same filtering capabilities as `list_executions/1` but returns only
the count of matching executions instead of loading the full execution records.

## Quick Example

```elixir
# Count all executions for a specific graph
count = Journey.count_executions(graph_name: "user_onboarding")

# Count executions where age > 18
adults_count = Journey.count_executions(
  graph_name: "user_registration",
  filter_by: [{:age, :gt, 18}]
)
```

## Parameters

  Please see `list_executions/1` for details on these parameters.

  * `options` - Keyword list of query options (all optional):
    * `:graph_name` - String name of a specific graph to filter by
    * `:graph_version` - String version of a specific graph to filter by (requires :graph_name)
    * `:filter_by` - List of node value filters (see `list_executions/1` for details)
    * `:include_archived` - Whether to include archived executions (default: false)

Note: `:sort_by`, `:limit`, and `:offset` are not supported for counting.

## Returns
* Non-negative integer representing the count of matching executions

## Key Behaviors
* **Database-level counting** - Uses SQL COUNT() for optimal performance
* **No record loading** - Never loads execution records, values, or computations
* **Same filtering** - Supports all the same filters as `list_executions/1`
* **Archived handling** - Excludes archived executions by default

## Examples

Basic counting by graph name:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "count example - #{Journey.Helpers.Random.random_string_w_time()}",
...>   "v1.0.0",
...>   [input(:status)]
...> )
iex> Journey.start(graph) |> Journey.set(:status, "active")
iex> Journey.start(graph) |> Journey.set(:status, "pending")
iex> Journey.start(graph) |> Journey.set(:status, "active")
iex> Journey.count_executions(graph_name: graph.name)
3
```

Counting with filters:

```elixir
iex> graph = Journey.Examples.Horoscope.graph()
iex> for day <- 1..20, do: Journey.start(graph) |> Journey.set(:birth_day, day) |> Journey.set(:birth_month, 4)
iex> Journey.count_executions(graph_name: graph.name, filter_by: [{:birth_day, :lte, 5}])
5
iex> Journey.count_executions(graph_name: graph.name, filter_by: [{:birth_day, :gt, 10}])
10
iex> Journey.count_executions(graph_name: graph.name, filter_by: [{:birth_day, :in, [5, 10, 15]}])
3
```

Counting with multiple filters:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "multi-filter count - #{Journey.Helpers.Random.random_string_w_time()}",
...>   "v1.0.0",
...>   [input(:age), input(:status)]
...> )
iex> Journey.start(graph) |> Journey.set(:age, 25) |> Journey.set(:status, "active")
iex> Journey.start(graph) |> Journey.set(:age, 17) |> Journey.set(:status, "active")
iex> Journey.start(graph) |> Journey.set(:age, 30) |> Journey.set(:status, "inactive")
iex> Journey.count_executions(
...>   graph_name: graph.name,
...>   filter_by: [{:age, :gte, 18}, {:status, :eq, "active"}]
...> )
1
```

Including archived executions:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "archived count - #{Journey.Helpers.Random.random_string_w_time()}",
...>   "v1.0.0",
...>   [input(:data)]
...> )
iex> e1 = Journey.start(graph)
iex> _e2 = Journey.start(graph)
iex> Journey.archive(e1)
iex> Journey.count_executions(graph_name: graph.name)
1
iex> Journey.count_executions(graph_name: graph.name, include_archived: true)
2
```

Pagination example (combining count and list):

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "pagination - #{Journey.Helpers.Random.random_string_w_time()}",
...>   "v1.0.0",
...>   [input(:index)]
...> )
iex> for i <- 1..25, do: Journey.start(graph) |> Journey.set(:index, i)
iex> total = Journey.count_executions(graph_name: graph.name)
iex> page_size = 10
iex> total_pages = div(total + page_size - 1, page_size)
iex> total_pages
3
iex> page_1 = Journey.list_executions(graph_name: graph.name, limit: page_size, offset: 0)
iex> length(page_1)
10
```

# `find_or_start`

Returns an existing execution for a singleton graph, or creates a new one if none exists.

This function implements the singleton pattern for executions, ensuring that only one
non-archived execution exists per graph name. Useful for workflows that represent
a single global process rather than per-user or per-request workflows.

Uses PostgreSQL advisory locks to prevent race conditions when multiple processes
attempt to access the singleton execution simultaneously.

## Quick Example

```elixir
graph = Journey.new_graph(
  "global config",
  "v1.0.0",
  [input(:setting_a), input(:setting_b)],
  singleton: true
)

# First call creates the execution
execution1 = Journey.find_or_start(graph)

# Subsequent calls return the same execution
execution2 = Journey.find_or_start(graph)
execution1.id == execution2.id  # true
```

## Parameters
* `graph` - A `%Journey.Graph{}` struct created with `new_graph/3` and `singleton: true`

## Returns
* `%Journey.Persistence.Schema.Execution{}` - The singleton execution for this graph

## Key Behaviors
* **Singleton per graph name** - Only one non-archived execution per graph name
* **Race-condition safe** - Uses PostgreSQL advisory locks for concurrent access
* **Excludes archived** - Archived executions are not considered; archiving allows a new singleton
* **Version independent** - Matches by graph name only, not version

## Examples

Basic singleton usage:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "singleton test - aGH7YaA0vAZL1780908257678911",
...>   "v1.0.0",
...>   [input(:value)],
...>   singleton: true
...> )
iex> e1 = Journey.find_or_start(graph)
iex> e2 = Journey.find_or_start(graph)
iex> e1.id == e2.id
true
```

State is preserved across calls:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "state test - Z3J9Ml3JRJmG1780908257678918",
...>   "v1.0.0",
...>   [input(:counter)],
...>   singleton: true
...> )
iex> e1 = Journey.find_or_start(graph)
iex> Journey.set(e1, :counter, 42)
iex> e2 = Journey.find_or_start(graph)
iex> {:ok, 42, _} = Journey.get(e2, :counter)
```

Concurrent access returns the same execution:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "concurrent test - AeMd4yxv8j551780908257678924",
...>   "v1.0.0",
...>   [input(:data)],
...>   singleton: true
...> )
iex> tasks = for _ <- 1..5, do: Task.async(fn -> Journey.find_or_start(graph) end)
iex> executions = Task.await_many(tasks)
iex> executions |> Enum.map(fn e -> e.id end) |> Enum.uniq() |> length()
1
```

# `history`

Returns the chronological history of all successful computations and set values for an execution.

This function provides visibility into the order of operations during execution, showing both
value sets and successful computations in chronological order. Only successful computations
are included; failed computations are filtered out. At the same revision, computations appear
before values.

## Quick Example

```elixir
history = Journey.history(execution)
# [%{node_name: :x, computation_or_value: :value, revision: 1},
#  %{node_name: :sum, computation_or_value: :computation, revision: 2}, ...]
```

Use `values/2` to see only current values, or `set/3` and `get_value/3` for individual operations.

## Parameters
* `execution` - A `%Journey.Persistence.Schema.Execution{}` struct or execution ID string

## Errors
* Raises if the supplied execution ID does not correspond to an existing execution

## Returns
* List of maps sorted by revision, where each map contains:
  * `:computation_or_value` - either `:computation` or `:value`
  * `:node_name` - the name of the node
  * `:node_type` - the type of the node (`:input`, `:compute`, `:mutate`, etc.)
  * `:revision` - the execution revision when this operation completed
  * `:value` - the actual value (only present for `:value` entries)

## Examples

Basic usage showing value sets and computation:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph("history example", "v1.0.0", [
...>   input(:x),
...>   input(:y),
...>   compute(:sum, [:x, :y], fn %{x: x, y: y} -> {:ok, x + y} end)
...> ])
iex> execution = Journey.start(graph)
iex> execution = Journey.set(execution, :x, 10)
iex> execution = Journey.set(execution, :y, 20)
iex> {:ok, 30, _revision} = Journey.get(execution, :sum, wait: :any)
iex> Journey.history(execution) |> Enum.map(fn entry ->
...>   case entry.node_name do
...>     :execution_id -> %{entry | value: "..."}
...>     :last_updated_at -> %{entry | value: 1234567890}
...>     _ -> entry
...>   end
...> end)
[
  %{node_name: :execution_id, node_type: :input, computation_or_value: :value, value: "...", revision: 0},
  %{node_name: :x, node_type: :input, computation_or_value: :value, value: 10, revision: 1},
  %{node_name: :y, node_type: :input, computation_or_value: :value, value: 20, revision: 2},
  %{node_name: :sum, node_type: :compute, computation_or_value: :computation, revision: 4},
  %{node_name: :last_updated_at, node_type: :input, computation_or_value: :value, value: 1234567890, revision: 4},
  %{node_name: :sum, node_type: :compute, computation_or_value: :value, value: 30, revision: 4}
]
```

# `list_executions`

Queries and retrieves multiple executions from the database with flexible filtering, sorting, and pagination.

This function enables searching across all executions in your system, with powerful filtering
capabilities based on graph names, node values, and execution metadata. It's essential for
monitoring workflows, building dashboards, and analyzing execution patterns.

## Quick Example

```elixir
# List all executions for a specific graph
executions = Journey.list_executions(graph_name: "user_onboarding")

# List executions for a specific graph version
v1_executions = Journey.list_executions(
  graph_name: "user_onboarding",
  graph_version: "v1.0.0"
)

# Find executions where age > 18
adults = Journey.list_executions(
  graph_name: "user_registration",
  filter_by: [{:age, :gt, 18}]
)
```

Use with `start/1` to create executions and `load/2` to get individual execution details.

## Parameters
  * `options` - Keyword list of query options (all optional):
    * `:graph_name` - String name of a specific graph to filter by
    * `:graph_version` - String version of a specific graph to filter by (requires :graph_name)
    * `:sort_by` - List of fields to sort by, including both execution fields and node values (see Sorting section for details)
    * `:filter_by` - List of node value filters using database-level filtering for optimal performance.

      Each filter is a tuple `{node_name, binary_operator, value}` or `{node_name, unary_operator}`.

      Binary Operators (require a comparison value):
      - comparisons: `:eq`, `:neq`, `:lt`, `:lte`, `:gt`, `:gte`
      - membership: `:in`, `:not_in`, `:contains` (case-sensitive substring matching, strings only), `:icontains` (case-insensitive substring matching, strings only), `:list_contains` (checks if a list-valued node contains the specified string or integer element)

      Unary Operators (no comparison value):
      - whether node was set: `:is_set`, `:is_not_set`

      For binary operators, values can be strings, numbers, booleans, nil or lists (used with `:in` and `:not_in`).
      Complex values (maps, tuples, functions) will raise an ArgumentError.
    * `:limit` - Maximum number of results (default: 10,000)
    * `:offset` - Number of results to skip for pagination (default: 0)
    * `:include_archived` - Whether to include archived executions (default: false)

## Returns
* List of `%Journey.Persistence.Schema.Execution{}` structs with preloaded values and computations
* Empty list `[]` if no executions match the criteria

## Options

### `:sort_by`
Sort by execution fields or node values. Supports atoms for ascending (`[:updated_at]`),
keywords for direction (`[updated_at: :desc]`), and mixed formats (`[:graph_name, inserted_at: :desc]`).

**Available fields:**
* Execution fields: `:inserted_at`, `:updated_at`, `:revision`, `:graph_name`, `:graph_version`
* Node values: Any node name from the graph (e.g., `:age`, `:score`) using JSONB ordering
* Direction: `:asc` (default) or `:desc`

## Key Behaviors
* Filtering performed at database level for optimal performance
* Only primitive values supported for filtering (complex types raise errors)
* Archived executions excluded by default

## Examples

Basic listing by graph name:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "list example basic - #{Journey.Helpers.Random.random_string_w_time()}",
...>   "v1.0.0",
...>   [input(:status)]
...> )
iex> Journey.start(graph) |> Journey.set(:status, "active")
iex> Journey.start(graph) |> Journey.set(:status, "pending")
iex> executions = Journey.list_executions(graph_name: graph.name)
iex> length(executions)
2
```

Filtering by graph version:

```elixir
iex> import Journey.Node
iex> graph_name = "version example JL55T0zLj8Ag1780908257678530"
iex> graph_v1 = Journey.new_graph(
...>   graph_name,
...>   "v1.0.0",
...>   [input(:data)]
...> )
iex> graph_v2 = Journey.new_graph(
...>   graph_name,
...>   "v2.0.0",
...>   [input(:data), input(:new_field)]
...> )
iex> Journey.start(graph_v1) |> Journey.set(:data, "v1 data")
iex> Journey.start(graph_v2) |> Journey.set(:data, "v2 data")
iex> Journey.list_executions(graph_name: graph_v1.name, graph_version: "v1.0.0") |> length()
1
iex> Journey.list_executions(graph_name: graph_v1.name, graph_version: "v2.0.0") |> length()
1
iex> Journey.list_executions(graph_name: graph_v1.name) |> length()
2
```

Validation that graph_version requires graph_name:

```elixir
iex> Journey.list_executions(graph_version: "v1.0.0")
** (ArgumentError) Option :graph_version requires :graph_name to be specified
```

Sorting by execution fields and node values:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "sort example - #{Journey.Helpers.Random.random_string_w_time()}",
...>   "v1.0.0",
...>   [input(:priority)]
...> )
iex> Journey.start(graph) |> Journey.set(:priority, "high")
iex> Journey.start(graph) |> Journey.set(:priority, "low")
iex> Journey.start(graph) |> Journey.set(:priority, "medium")
iex> # Sort by priority descending - shows the actual sorted values
iex> Journey.list_executions(graph_name: graph.name, sort_by: [priority: :desc]) |> Enum.map(fn e -> Journey.values(e) |> Map.get(:priority) end)
["medium", "low", "high"]
```

Filtering with multiple operators:

```elixir
iex> graph = Journey.Examples.Horoscope.graph()
iex> for day <- 1..20, do: Journey.start(graph) |> Journey.set(:birth_day, day) |> Journey.set(:birth_month, 4) |> Journey.set(:first_name, "Mario")
iex> # Various filtering examples
iex> Journey.list_executions(graph_name: graph.name, filter_by: [{:birth_day, :eq, 10}]) |> Enum.count()
1
iex> Journey.list_executions(graph_name: graph.name, filter_by: [{:birth_day, :neq, 10}]) |> Enum.count()
19
iex> Journey.list_executions(graph_name: graph.name, filter_by: [{:birth_day, :lte, 5}]) |> Enum.count()
5
iex> Journey.list_executions(graph_name: graph.name, filter_by: [{:birth_day, :in, [5, 10, 15]}]) |> Enum.count()
3
iex> Journey.list_executions(graph_name: graph.name, filter_by: [{:first_name, :is_set}]) |> Enum.count()
20
iex> Journey.list_executions(graph_name: graph.name, filter_by: [{:first_name, :contains, "ari"}]) |> Enum.count()
20
iex> Journey.list_executions(graph_name: graph.name, filter_by: [{:first_name, :icontains, "MARIO"}]) |> Enum.count()
20
```

List containment filtering with `:list_contains`:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "notification example - #{Journey.Helpers.Random.random_string_w_time()}",
...>   "v1.0.0",
...>   [input(:recipients)]
...> )
iex> Journey.start(graph) |> Journey.set(:recipients, ["user1", "user2", "admin"])
iex> Journey.start(graph) |> Journey.set(:recipients, ["user3", "user4"])
iex> Journey.start(graph) |> Journey.set(:recipients, [1, 2, 3])
iex> # Find executions where recipients list contains "user1"
iex> Journey.list_executions(graph_name: graph.name, filter_by: [{:recipients, :list_contains, "user1"}]) |> Enum.count()
1
iex> # Find executions where recipients list contains integer 2
iex> Journey.list_executions(graph_name: graph.name, filter_by: [{:recipients, :list_contains, 2}]) |> Enum.count()
1
```

Multiple filters, sorting, and pagination:

```elixir
iex> graph = Journey.Examples.Horoscope.graph()
iex> for day <- 1..20, do: Journey.start(graph) |> Journey.set(:birth_day, day) |> Journey.set(:birth_month, 4) |> Journey.set(:first_name, "Mario")
iex> # Multiple filters combined
iex> Journey.list_executions(
...>   graph_name: graph.name,
...>   filter_by: [{:birth_day, :gt, 10}, {:first_name, :is_set}],
...>   sort_by: [birth_day: :desc],
...>   limit: 5
...> ) |> Enum.count()
5
iex> # Pagination
iex> Journey.list_executions(graph_name: graph.name, limit: 3) |> Enum.count()
3
iex> Journey.list_executions(graph_name: graph.name, limit: 5, offset: 10) |> Enum.count()
5
```

Including archived executions:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "list example - archived - #{Journey.Helpers.Random.random_string_w_time()}",
...>   "v1.0.0",
...>   [input(:status)]
...> )
iex> e1 = Journey.start(graph)
iex> _e2 = Journey.start(graph)
iex> Journey.archive(e1)
iex> Journey.list_executions(graph_name: graph.name) |> length()
1
iex> Journey.list_executions(graph_name: graph.name, include_archived: true) |> length()
2
```

# `load`

Reloads the current state of an execution from the database to get the latest changes.

Executions can be modified by their background computations, or scheduled events, or other processes setting their values. This function is used to get the latest state of an execution -- as part of normal operations, or when the system starts up, or when the user whose session is being tracked as an execution comes back to the web site and resumes their flow.

## Quick Example

```elixir
execution = Journey.set(execution, :name, "Mario")
execution = Journey.load(execution)  # Get updated state with new revision
{:ok, greeting, _} = Journey.get(execution, :greeting, wait: :any)
```

Use `set/3` and `get_value/3` to modify and read execution values.

## Parameters
* `execution` - A `%Journey.Persistence.Schema.Execution{}` struct or execution ID string
* `opts` - Keyword list of options (see Options section below)

## Returns
* A `%Journey.Persistence.Schema.Execution{}` struct with current database state, or `nil` if not found

## Options
* `:preload` - Whether to preload associated nodes and values. Defaults to `true`.
  Set to `false` for better performance when you only need execution metadata.
* `:include_archived` - Whether to include archived executions. Defaults to `false`.
  Archived executions are normally hidden but can be loaded with this option.
* `:computations` - List of computation states to preload. Defaults to all states.
  Use `[:not_set, :computing]` to load only active computations for better performance
  on executions with large computation history (e.g., long-running `tick_recurring` nodes).

## Key Behaviors
* **Fresh state** - Always returns the current state from the database, not cached data
* **Revision tracking** - Loaded execution will have the latest revision number
* **Archived handling** - Archived executions return `nil` unless explicitly included
* **Performance option** - Use `preload: false` to skip loading values/computations for speed

## Examples

Basic reloading after value changes:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "load example - basic",
...>       "v1.0.0",
...>       [
...>         input(:name),
...>         compute(:greeting, [:name], fn %{name: name} -> {:ok, "Hello, #{name}!"} end)
...>       ]
...>     )
iex> execution = Journey.start(graph)
iex> execution.revision
0
iex> execution = Journey.set(execution, :name, "Alice")
iex> execution.revision > 0
true
iex> {:ok, "Hello, Alice!", _} = Journey.get(execution, :greeting, wait: :any)
iex> reloaded = Journey.load(execution)
iex> reloaded.revision >= execution.revision
true
```

Loading by execution ID:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "load example - by id",
...>       "v1.0.0",
...>       [input(:data)]
...>     )
iex> execution = Journey.start(graph)
iex> execution_id = execution.id
iex> reloaded = Journey.load(execution_id)
iex> reloaded.id == execution_id
true
```

Performance optimization with preload option:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "load example - no preload",
...>       "v1.0.0",
...>       [input(:data)]
...>     )
iex> execution = Journey.start(graph)
iex> fast_load = Journey.load(execution, preload: false)
iex> fast_load.id == execution.id
true
```

Handling archived executions:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "load example - archived",
...>       "v1.0.0",
...>       [input(:data)]
...>     )
iex> execution = Journey.start(graph)
iex> Journey.archive(execution)
iex> Journey.load(execution)
nil
iex> Journey.load(execution, include_archived: true) != nil
true
```

# `start`

Starts a new execution instance of a computation graph, initializing it to accept input values and perform computations.

Creates a persistent execution in the database with a unique ID and begins background processing
for any schedulable nodes. The execution starts with revision 0 and no values set.

## Quick Example

```elixir
execution = Journey.start(graph)
execution = Journey.set(execution, :name, "Mario")
{:ok, greeting, _} = Journey.get(execution, :greeting, wait: :any)
```

Use `set/3` to provide input values and `get/3` to retrieve computed results.

## Parameters
* `graph` - A validated `%Journey.Graph{}` struct created with `new_graph/3`. The graph must
  have passed validation during creation and be registered in the graph catalog.

## Returns
* A new `%Journey.Persistence.Schema.Execution{}` struct with:
  * `:id` - Unique execution identifier (UUID string)
  * `:graph_name` and `:graph_version` - From the source graph
  * `:revision` - Always starts at 0, increments with each state change
  * `:archived_at` - Initially nil (not archived)
  and other fields.

## Key Behaviors
* **Database persistence** - Execution state is immediately saved to PostgreSQL
* **Unique execution** - Each call creates a completely independent execution instance
* **Background processing** - Scheduler automatically begins monitoring for schedulable nodes
* **Ready for inputs** - Can immediately accept input values via `set/3`

## Singleton Graphs
For graphs created with `singleton: true`, use `find_or_start/1` instead.
Calling `start/1` on a singleton graph will raise an `ArgumentError`.

## Examples

Basic execution creation:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "greeting workflow",
...>       "v1.0.0",
...>       [
...>         input(:name),
...>         compute(
...>           :greeting,
...>           [:name],
...>           fn %{name: name} -> {:ok, "Hello, #{name}!"} end
...>         )
...>       ]
...>     )
iex> execution = Journey.start(graph)
iex> execution.graph_name
"greeting workflow"
iex> execution.graph_version
"v1.0.0"
iex> execution.revision
0
```

Execution properties and immediate workflow:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "calculation workflow",
...>       "v1.0.0",
...>       [
...>         input(:x),
...>         input(:y),
...>         compute(:sum, [:x, :y], fn %{x: x, y: y} -> {:ok, x + y} end)
...>       ]
...>     )
iex> execution = Journey.start(graph)
iex> is_binary(execution.id)
true
iex> execution.archived_at
nil
iex> user_values = Journey.values(execution, reload: false) |> Map.drop([:execution_id, :last_updated_at])
iex> user_values
%{}
iex> execution = Journey.set(execution, :x, 10)
iex> execution = Journey.set(execution, :y, 20)
iex> {:ok, 30, _revision} = Journey.get(execution, :sum, wait: :any)
```

Multiple independent executions:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "counter workflow",
...>       "v1.0.0",
...>       [input(:count)]
...>     )
iex> execution1 = Journey.start(graph)
iex> execution2 = Journey.start(graph)
iex> execution1.id != execution2.id
true
iex> execution1 = Journey.set(execution1, :count, 1)
iex> execution2 = Journey.set(execution2, :count, 2)
iex> {:ok, 1, 1} = Journey.get(execution1, :count)
iex> {:ok, 2, 1} = Journey.get(execution2, :count)
```

# `unarchive`

Un-archives the supplied execution, if it is archived.

## Parameters:
- `execution` or `execution_id`: The execution to un-archive, or the ID of the execution to un-archive.

## Errors
* Raises if the supplied execution ID does not correspond to an existing execution

## Returns
* :ok

## Examples

  ```elixir
  iex> execution =
  ...>    Journey.Examples.Horoscope.graph() |>
  ...>    Journey.start() |>
  ...>    Journey.set(:birth_day, 26)
  iex> _archived_at = Journey.archive(execution)
  iex> # The execution is now archived, and it is no longer visible.
  iex> nil == Journey.load(execution, include_archived: false)
  true
  iex> Journey.unarchive(execution)
  :ok
  iex> # The execution is now un-archived, and it can now be loaded.
  iex> nil == Journey.load(execution, include_archived: false)
  false
  iex> # Un-archiving an un-archived execution has no effect.
  iex> Journey.unarchive(execution)
  :ok
  ```

# `get`

Returns the value and revision of a node in an execution. Optionally waits for the value to be set.

This function atomically returns both the node value and its revision number, eliminating
race conditions when you need to track which revision of a value you received.

## Quick Examples

```elixir
# Basic usage - get a set value and its revision immediately
{:ok, value, revision} = Journey.get(execution, :name)

# Wait for a computed value to be available (30 second default timeout)
{:ok, result, revision} = Journey.get(execution, :computed_field, wait: :any)

# Wait for a new version of the value with custom timeout
{:ok, new_value, new_revision} = Journey.get(execution, :name, wait: :newer, timeout: 5000)

# Wait for a value newer than a specific revision
{:ok, fresh_value, fresh_revision} = Journey.get(execution, :name, wait: {:newer_than, 10})
```

Use `set/3` to set input values that trigger computations.

## Parameters
* `execution` - A `%Journey.Persistence.Schema.Execution{}` struct or a binary execution ID
* `node_name` - Atom representing the node name (must exist in the graph)
* `opts` - Keyword list of options (see Options section below)

## Returns
* `{:ok, value, revision}` – the value is set, with its revision number
* `{:error, :not_set}` – the value is not yet set
* `{:error, :computation_failed}` – the computation permanently failed

## Errors
* Raises if the supplied execution ID does not correspond to an existing execution
* Raises `RuntimeError` if the node name does not exist in the execution's graph
* Raises `ArgumentError` if an invalid `:wait` option is provided
* Raises `ArgumentError` if `wait: :newer` is used with a binary execution ID

## Options
* `:wait` – Controls waiting behavior:
  * `:immediate` (default) – Return immediately without waiting
  * `:any` – Wait until the value is available or timeout
  * `:newer` – Wait for a newer revision than current execution (requires `%Execution{}` struct)
  * `{:newer_than, revision}` – Wait for value newer than specific revision
* `:timeout` – Timeout in milliseconds (default: 30,000) or `:infinity`

## Examples
  ```elixir
  iex> execution =
  ...>    Journey.Examples.Horoscope.graph() |>
  ...>    Journey.start() |>
  ...>    Journey.set(:birth_day, 26)
  iex> {:ok, 26, _revision} = Journey.get(execution, :birth_day)
  iex> Journey.get(execution, :birth_month)
  {:error, :not_set}
  iex> Journey.get(execution, :astrological_sign)
  {:error, :not_set}
  iex> execution = Journey.set(execution, :birth_month, "April")
  iex> Journey.get(execution, :astrological_sign)
  {:error, :not_set}
  iex> {:ok, "Taurus", _revision} = Journey.get(execution, :astrological_sign, wait: :any)
  iex> Journey.get(execution, :horoscope, wait: :any, timeout: 2_000)
  {:error, :not_set}
  iex> execution = Journey.set(execution, :first_name, "Mario")
  iex> {:ok, "🍪s await, Taurus Mario!", _revision} = Journey.get(execution, :horoscope, wait: :any)
  ```

# `set`

Sets values for input nodes in an execution and triggers recomputation of dependent nodes.

This function supports three calling patterns:
1. Single value: `set(execution, :node_name, value)`
2. Multiple values via map: `set(execution, %{node1: value1, node2: value2})`
3. Multiple values via keyword list: `set(execution, node1: value1, node2: value2)`

When values are set, Journey automatically recomputes any dependent computed nodes to ensure
consistency across the dependency graph. The operation is idempotent - setting the same values
has no effect.

## Parameters

**Single value:**
* `execution` - A `%Journey.Persistence.Schema.Execution{}` struct or execution ID string
* `node_name` - Atom representing the input node name (must exist in the graph)
* `value` - The value to set. Supported types: nil, string, number, map, list, boolean. Note that if the map or the list contains atoms, those atoms will be converted to strings.

**Multiple values:**
* `execution` - A `%Journey.Persistence.Schema.Execution{}` struct or execution ID string
* `values` - Map of node names to values (e.g., `%{node1: "value1", node2: 42}`) or keyword list (e.g., `[node1: "value1", node2: 42]`)

## Options
* `metadata:` - Optional contextual information to attach to the value(s).
  Accepts any JSON-compatible type: `nil`, string, number, boolean, list, or map.
  If using a map, **keys must be strings** (not atoms) for JSONB storage.
  Useful for audit trails, tracking authors, timestamps, IP addresses, or other provenance data.
  For bulk operations (map/keyword list), the same metadata applies to all values.
  Metadata is stored with the value and flows to historians and compute functions but is not exposed via `Journey.get()`.
  Default: `nil`

## Returns
* Updated `%Journey.Persistence.Schema.Execution{}` struct with incremented revision (if any value changed)

## Errors
* Raises if the supplied execution ID does not correspond to an existing execution
* Raises `RuntimeError` if any node name does not exist in the execution's graph
* Raises `RuntimeError` if attempting to set compute nodes (only input nodes can be set)

## Key Behaviors
* **Automatic recomputation** - Setting values triggers recomputation of all dependent nodes
* **Idempotent** - Setting the same values has no effect (no revision increment)
* **Input nodes only** - Only input nodes can be set; compute nodes are read-only
* **Atomic updates** - Multiple values are set together in a single transaction (single revision increment)
* **Metadata tracking** - Optional metadata flows to historians and arity-2 compute functions for audit trails

## Quick Examples

```elixir
# Single value
execution = Journey.set(execution, :name, "Mario")

# Multiple values via map
execution = Journey.set(execution, %{name: "Mario", age: 35})

# Multiple values via keyword list
execution = Journey.set(execution, name: "Mario", age: 35)

{:ok, greeting, _} = Journey.get(execution, :greeting, wait: :any)
```

Use `get_value/3` to retrieve values and `unset/2` to remove values.

## Examples

Basic setting with cascading recomputation:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "set workflow - cascading example",
...>       "v1.0.0",
...>       [
...>         input(:name),
...>         compute(:greeting, [:name], fn %{name: name} -> {:ok, "Hello, #{name}!"} end)
...>       ]
...>     )
iex> execution = graph |> Journey.start()
iex> execution = Journey.set(execution, :name, "Mario")
iex> {:ok, "Hello, Mario!", rev1} = Journey.get(execution, :greeting, wait: :any)
iex> execution = Journey.set(execution, :name, "Luigi")
iex> {:ok, "Hello, Luigi!", _revision} = Journey.get(execution, :greeting, wait: {:newer_than, rev1})
```

Idempotent behavior - same value doesn't change revision:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "set workflow - idempotent example",
...>       "v1.0.0",
...>       [input(:name)]
...>     )
iex> execution = graph |> Journey.start()
iex> execution = Journey.set(execution, :name, "Mario")
iex> first_revision = execution.revision
iex> execution = Journey.set(execution, :name, "Mario")
iex> execution.revision == first_revision
true
```

Different value types:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "set workflow - value types example",
...>       "v1.0.0",
...>       [input(:number), input(:flag), input(:data)]
...>     )
iex> execution = graph |> Journey.start()
iex> execution = Journey.set(execution, :number, 42)
iex> execution = Journey.set(execution, :flag, true)
iex> execution = Journey.set(execution, :data, %{"key" => "value"})
iex> {:ok, 42, _revision} = Journey.get(execution, :number)
iex> {:ok, true, _revision} = Journey.get(execution, :flag)
```

Using an execution ID:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "set workflow - execution_id example",
...>       "v1.0.0",
...>       [input(:name)]
...>     )
iex> execution = graph |> Journey.start()
iex> updated_execution = Journey.set(execution.id, :name, "Luigi")
iex> {:ok, "Luigi", _revision} = Journey.get(updated_execution, :name)
```

Multiple values via map (atomic operation):

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "set workflow - multiple map example",
...>       "v1.0.0",
...>       [
...>         input(:first_name),
...>         input(:last_name),
...>         compute(:full_name, [:first_name, :last_name], fn %{first_name: first, last_name: last} ->
...>           {:ok, "#{first} #{last}"}
...>         end)
...>       ]
...>     )
iex> execution = graph |> Journey.start()
iex> execution = Journey.set(execution, %{first_name: "Mario", last_name: "Bros"})
iex> {:ok, "Mario", 1} = Journey.get(execution, :first_name)
iex> {:ok, "Bros", 1} = Journey.get(execution, :last_name)
iex> {:ok, "Mario Bros", 3} = Journey.get(execution, :full_name, wait: :any)
```

Multiple values via keyword list (ergonomic syntax):

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "set workflow - keyword example",
...>       "v1.0.0",
...>       [input(:name), input(:age), input(:active)]
...>     )
iex> execution = graph |> Journey.start()
iex> execution = Journey.set(execution, name: "Mario", age: 35, active: true)
iex> {:ok, "Mario", 1} = Journey.get(execution, :name)
iex> {:ok, 35, 1} = Journey.get(execution, :age)
iex> {:ok, true, 1} = Journey.get(execution, :active)
```

Setting values with metadata for audit trails:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "audit trail example",
...>       "v1.0.0",
...>       [
...>         input(:document_title),
...>         historian(:title_history, [:document_title])
...>       ]
...>     )
iex> execution = graph |> Journey.start()
iex> execution = Journey.set(execution, :document_title, "Draft v1", metadata: %{"author_id" => "user123"})
iex> {:ok, history1, history1_rev} = Journey.get(execution, :title_history, wait: :any)
iex> length(history1)
1
iex> execution = Journey.set(execution, :document_title, "Draft v2", metadata: %{"author_id" => "user456"})
iex> {:ok, history2, _} = Journey.get(execution, :title_history, wait: {:newer_than, history1_rev})
iex> length(history2)
2
iex> # History entries include metadata for audit trail (newest first)
iex> [%{"value" => "Draft v2", "metadata" => %{"author_id" => "user456"}}, %{"value" => "Draft v1", "metadata" => %{"author_id" => "user123"}}] = history2
```

Metadata with different types:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "metadata types example",
...>       "v1.0.0",
...>       [input(:field)]
...>     )
iex> execution = graph |> Journey.start()
iex> # String metadata
iex> execution = Journey.set(execution, :field, "value1", metadata: "version-1")
iex> # Map metadata (keys must be strings, not atoms)
iex> execution = Journey.set(execution, :field, "value2", metadata: %{"author_id" => "user789", "ip" => "192.168.1.1"})
iex> # Number metadata
iex> execution = Journey.set(execution, :field, "value3", metadata: 42)
iex> # List metadata
iex> execution = Journey.set(execution, :field, "value4", metadata: ["tag1", "tag2"])
iex> {:ok, "value4", _} = Journey.get(execution, :field)
```

# `unset`

Removes values from input nodes in an execution and invalidates all dependent computed nodes.

This function supports two calling patterns:
1. Single value: `unset(execution, :node_name)`
2. Multiple values via list: `unset(execution, [:node1, :node2, :node3])`

When values are unset, Journey automatically invalidates (unsets) all computed nodes that depend
on the unset inputs, creating a cascading effect through the dependency graph. This ensures data
consistency - no computed values remain that were based on the now-removed inputs.

## Quick Examples

```elixir
# Single value
execution = Journey.unset(execution, :name)
{:error, :not_set} = Journey.get(execution, :name)

# Multiple values
execution = Journey.unset(execution, [:first_name, :last_name, :email])
```

Use `set/3` to set values and `get_value/3` to check if values are set.

## Parameters

**Single value:**
* `execution` - A `%Journey.Persistence.Schema.Execution{}` struct or execution ID string
* `node_name` - Atom representing the input node name (must exist in the graph)

**Multiple values:**
* `execution` - A `%Journey.Persistence.Schema.Execution{}` struct or execution ID string
* `node_names` - List of atoms representing input node names (all must exist in the graph)

## Returns
* Updated `%Journey.Persistence.Schema.Execution{}` struct with incremented revision (if value was set)

## Errors
* Raises if the supplied execution ID does not correspond to an existing execution
* Raises `RuntimeError` if the node name does not exist in the execution's graph
* Raises `RuntimeError` if attempting to unset a compute node (only input nodes can be unset)

## Key Behaviors
* **Cascading invalidation** - Dependent computed nodes are automatically unset
* **Idempotent** - Multiple unsets of the same value have no additional effect
* **Input nodes only** - Only input nodes can be unset; compute nodes cannot be unset
* **Atomic updates** - Multiple values are unset together in a single transaction (single revision increment)

## Examples

Basic unsetting with cascading invalidation:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "unset workflow - basic example",
...>       "v1.0.0",
...>       [
...>         input(:name),
...>         compute(
...>           :greeting,
...>           [:name],
...>           fn %{name: name} -> {:ok, "Hello, #{name}!"} end
...>         )
...>       ]
...>     )
iex> execution = graph |> Journey.start()
iex> execution = Journey.set(execution, :name, "Mario")
iex> {:ok, "Hello, Mario!", 3} = Journey.get(execution, :greeting, wait: :any)
iex> execution_after_unset = Journey.unset(execution, :name)
iex> Journey.get(execution_after_unset, :name)
{:error, :not_set}
iex> Journey.get(execution_after_unset, :greeting)
{:error, :not_set}
```

Multi-level cascading (A → B → C chain):

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>       "unset workflow - cascade example",
...>       "v1.0.0",
...>       [
...>         input(:a),
...>         compute(:b, [:a], fn %{a: a} -> {:ok, "B:#{a}"} end),
...>         compute(:c, [:b], fn %{b: b} -> {:ok, "C:#{b}"} end)
...>       ]
...>     )
iex> execution = graph |> Journey.start()
iex> execution = Journey.set(execution, :a, "value")
iex> {:ok, "B:value", 3} = Journey.get(execution, :b, wait: :any)
iex> {:ok, "C:B:value", 5} = Journey.get(execution, :c, wait: :any)
iex> execution_after_unset = Journey.unset(execution, :a)
iex> Journey.get(execution_after_unset, :a)
{:error, :not_set}
iex> Journey.get(execution_after_unset, :b)
{:error, :not_set}
iex> Journey.get(execution_after_unset, :c)
{:error, :not_set}
```

Idempotent behavior:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "unset workflow - idempotent example",
...>   "v1.0.0",
...>   [input(:name)]
...> )
iex> execution = graph |> Journey.start()
iex> original_revision = execution.revision
iex> execution_after_unset = Journey.unset(execution, :name)
iex> execution_after_unset.revision == original_revision
true
```

Multiple values atomic operation:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph(
...>   "unset workflow - multiple values example",
...>   "v1.0.0",
...>   [
...>     input(:first_name),
...>     input(:last_name),
...>     input(:email),
...>     compute(:full_name, [:first_name, :last_name], fn %{first_name: first_name, last_name: last_name} ->
...>       {:ok, "#{first_name} #{last_name}"}
...>     end)
...>   ]
...> )
iex> execution = graph |> Journey.start()
iex> execution = Journey.set(execution, %{first_name: "Mario", last_name: "Bros", email: "mario@example.com"})
iex> {:ok, "Mario Bros", 3} = Journey.get(execution, :full_name, wait: :any)
iex> execution_after_unset = Journey.unset(execution, [:first_name, :last_name])
iex> Journey.get(execution_after_unset, :first_name)
{:error, :not_set}
iex> Journey.get(execution_after_unset, :last_name)
{:error, :not_set}
iex> {:ok, "mario@example.com", 1} = Journey.get(execution_after_unset, :email)
iex> Journey.get(execution_after_unset, :full_name)
{:error, :not_set}
```

# `values`

Returns a map of node values in an execution.

By default, only returns nodes that have been set, excluding unset nodes.
With `include_unset_as_nil: true`, returns all nodes with unset ones as `nil`.
Always includes `:execution_id` and `:last_updated_at` metadata.

## Quick Example

```elixir
execution = Journey.set(execution, :name, "Alice")
values = Journey.values(execution)
# %{name: "Alice", execution_id: "EXEC...", last_updated_at: 1234567890}

# Include unset nodes as nil
all_values = Journey.values(execution, include_unset_as_nil: true)
# %{name: "Alice", age: nil, execution_id: "EXEC...", last_updated_at: 1234567890}
```

Use `values_all/1` to see all nodes with their status tuples, or `get_value/3` for individual values.

## Parameters
* `execution` - A `%Journey.Persistence.Schema.Execution{}` struct or a binary execution ID
* `opts` - Keyword list of options:
  * `:reload` - Reload execution from database (default: `true`). Only valid when passing
    an `%Execution{}` struct. Raises `ArgumentError` if used with a binary execution ID,
    since the execution is always loaded fresh from the database in that case.
  * `:include_unset_as_nil` - Include unset nodes as `nil` values (default: `false`)

## Returns
* Map with node names as keys and their current values as values
* When `include_unset_as_nil: false` (default): Only includes set nodes
* When `include_unset_as_nil: true`: Includes all nodes, with unset ones as `nil`

## Errors
* Raises if the supplied execution ID does not correspond to an existing execution

## Examples

Basic usage:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph("example", "v1.0.0", [input(:name), input(:age)])
iex> execution = Journey.start(graph)
iex> Journey.values(execution) |> redact([:execution_id, :last_updated_at])
%{execution_id: "...", last_updated_at: 1234567890}
iex> execution = Journey.set(execution, :name, "Alice")
iex> Journey.values(execution) |> redact([:execution_id, :last_updated_at])
%{name: "Alice", execution_id: "...", last_updated_at: 1234567890}
```

Including unset nodes:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph("example", "v1.0.0", [input(:name), input(:age)])
iex> execution = Journey.start(graph)
iex> execution = Journey.set(execution, :name, "Alice")
iex> Journey.values(execution, include_unset_as_nil: true) |> redact([:execution_id, :last_updated_at])
%{name: "Alice", age: nil, execution_id: "...", last_updated_at: 1234567890}
```

Passing a binary execution ID:

```elixir
Journey.values(execution.id, include_unset_as_nil: true)
```

# `values_all`

Returns a map of all nodes in an execution with their current status, including unset nodes.

Unlike `values/2` which only returns set nodes, this function shows all nodes including those
that haven't been set yet. Unset nodes are marked as `:not_set`, while set nodes are returned
as `{:set, value}` tuples. Useful for debugging and introspection.

## Quick Example

```elixir
all_status = Journey.values_all(execution)
# %{name: {:set, "Alice"}, age: :not_set, execution_id: {:set, "EXEC..."}, ...}
```

Use `values/2` to get only set values, or `get_value/3` for individual node values.

## Parameters
* `execution` - A `%Journey.Persistence.Schema.Execution{}` struct or a binary execution ID
* `opts` - Keyword list of options:
  * `:reload` - Reload execution from database (default: `true`). Only valid when passing
    an `%Execution{}` struct. Raises `ArgumentError` if used with a binary execution ID,
    since the execution is always loaded fresh from the database in that case.

## Returns
* Map with all nodes showing status: `:not_set` or `{:set, value}`
* Includes all nodes defined in the graph, regardless of current state

## Errors
* Raises if the supplied execution ID does not correspond to an existing execution

## Examples

Basic usage showing status progression:

```elixir
iex> import Journey.Node
iex> graph = Journey.new_graph("example", "v1.0.0", [input(:name), input(:age)])
iex> execution = Journey.start(graph)
iex> Journey.values_all(execution) |> redact([:execution_id, :last_updated_at])
%{name: :not_set, age: :not_set, execution_id: {:set, "..."}, last_updated_at: {:set, 1234567890}}
iex> execution = Journey.set(execution, :name, "Alice")
iex> Journey.values_all(execution) |> redact([:execution_id, :last_updated_at])
%{name: {:set, "Alice"}, age: :not_set, execution_id: {:set, "..."}, last_updated_at: {:set, 1234567890}}
```

Passing a binary execution ID:

```elixir
Journey.values_all(execution.id)
```

# `get_value`

  Deprecated, use `Journey.get/3` instead"

# `set_value`

> This function is deprecated. Use Journey.set/2 instead.

# `set_value`

> This function is deprecated. Use Journey.set/3 instead.

# `start_execution`

Use `start/1` instead.

# `unset_value`

> This function is deprecated. Use Journey.unset/2 instead.

---

*Consult [api-reference.md](api-reference.md) for complete listing*