docs: port architecture specs + 45 ADRs from alknet, renumbered
Port the call + channels architecture documentation from the alknet mono-repo into docs/architecture/, renumbered as alkcall ADR-001..045. Renumbering map (alknet -> alkcall): Core: 001,002,004,006,007,011,065,070,092,014,050,091 -> 001-012 Call: 005,064,012,023,015,022,024,016,049,017,028,029,030,032,066,069,067,068 -> 013-030 Shared: 003,009,013 -> 031-033 Channels: 071,093,072,073,074,075,076,094,079,080,081,089 -> 034-045 3 superseded/reversed ADRs kept for historical trail: - ADR-013 (irpc foundation, superseded by ADR-014) - ADR-023 (peer-scoped filtering, superseded by ADR-024) - ADR-077 (TTY inside channels, reversed by ADR-035 — not ported, TTY-only) Ported docs (11 spec files + README + open-questions): - call-README.md, call-protocol.md, operation-registry.md, client-and-adapters.md - channels-README.md, channels-overview.md, channels-wire.md, channels-connection.md, channels-adapter.md, channel-operations.md, channel-client.md - README.md (index with doc table, ADR table grouped by category, key principles) - open-questions.md (lean — 30 OQs, renumbered OQ-01..030; includes new OQ-22 for the pub/sub gap) Cross-reference rewriting: - All ADR-NNN references rewritten single-pass (no chaining bug) - Markdown link paths fixed - Title lines aligned with filenames - Non-ported ADR refs (052, 082, 086, etc.) left as-is with README note The open-questions.md includes OQ-22 (new): the call protocol pub/sub gap — subscribe exists but pub does not, needed for channels channel/resources/subscribe fan-out. This is the next ADR to write (alkcall ADR-046).
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# ADR-020: Abort Cascade for Nested Calls
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## Status
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Accepted
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## Context
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The call protocol allows handlers to compose other operations through
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`OperationEnv::invoke()`. This creates a call tree: a parent request spawns
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children (via `parent_request_id`), which may spawn their own children. The
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tree is the agency chain (ADR-017) — principal delegates to agent, agent may
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delegate to sub-agent.
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When `call.aborted` arrives for a parent request, the current `PendingRequestMap`
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removes only that single entry. The children are unaware — they continue running,
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consuming resources, and potentially producing side effects. This is the nested
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abort problem:
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```
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Client calls /agent/chat (r1)
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agent handler calls /fs/readFile via env.invoke (r1-a)
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fs handler calls /db/query via env.invoke (r1-a-1)
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agent handler calls /bash/exec via env.invoke (r1-b)
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Client aborts r1 (call.aborted { id: "r1" })
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→ r1 removed from PendingRequestMap
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→ r1-a, r1-a-1, r1-b continue running (ghost work)
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→ bash/exec keeps executing (unwanted side effect)
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→ db/query keeps running (wasted resources)
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→ results produced that nobody consumes
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```
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The `@alkdev/flowgraph` TypeScript package solved this with a directed graph
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that tracks the call tree and a `FailurePolicy` enum:
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- `"abort-dependents"`: aborting a node cascades to all non-terminal descendants.
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This is the "whole tree should abort" behavior.
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- `"continue-running"`: only idle/waiting dependents are aborted; started ones
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keep going. New ones don't start because their predecessors failed/aborted.
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The agent use case makes this concrete and urgent: an LLM composes deep, dynamic
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call trees (parallel tools, sequential tools, sub-agents calling sub-tools).
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Aborting a chat should tear down the entire tree — the LLM HTTP stream, all tool
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calls, all sub-calls. But this is a protocol-level concern, not an agent feature:
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every consumer (NAPI adapter, Python adapter, any service speaking EventEnvelope)
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inherits whatever abort model the protocol defines. The call protocol is a
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general-purpose cross-boundary RPC mechanism; nested composition is a core
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protocol feature, and abort semantics for that composition are protocol semantics.
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## Decision
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### 1. `call.aborted` cascades to descendants
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When `call.aborted` arrives for a request, the protocol cascades the abort to
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all non-terminal descendants in the call tree (identified via `parent_request_id`).
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Each descendant receives a `call.aborted` event. The `PendingRequestMap` removes
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all affected entries.
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The cascade is protocol-level: the event schema carries cascade semantics. A
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`call.aborted` for a parent implies abort of all descendants. This is not a
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client-side convention — the server (CallAdapter) is responsible for discovering
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descendants and propagating the abort.
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### 2. Default policy: `abort-dependents`
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The default policy is `abort-dependents`: aborting a request aborts everything
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downstream, regardless of branch. This is the correct default because aborted
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parent work has no consumer waiting for results — continuing is wasted work at
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best and unwanted side effects at worst (e.g., a `bash/exec` that keeps running
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after the caller stopped caring, a DB mutation that completes after the
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transaction was aborted).
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### 3. Opt-in policy: `continue-running`
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An opt-in `continue-running` policy is available for cases where long-running
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work should survive a parent's abort. Under `continue-running`:
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- Descendants that have already started (status: running) continue to completion.
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- Descendants that haven't started yet (status: pending/waiting) are aborted
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(their predecessors failed, so they can't proceed).
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- No new descendants start (the parent is gone).
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Use cases for `continue-running`: a long-running subscription that should keep
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streaming after its parent's sibling failed; a background task that was spawned
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by a handler and should survive the handler's abort.
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The caller or handler specifies the policy at call time. The policy is set
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on the `OperationContext` and propagated to children via `OperationEnv::invoke()`
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— see Decision 6 below. The default is `abort-dependents`; `continue-running`
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is an opt-in for long-running work that should survive a parent's abort.
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### 4. Cleanup hooks
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When a call is aborted, handlers need a mechanism to clean up resources: cancel
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an HTTP stream, cancel a honker queue job, close a file handle, release a lock.
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The protocol provides this through the call lifecycle — when a call is aborted,
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the handler's task is cancelled (in Rust, the future is dropped). Cleanup is
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handled by `Drop` implementations on resource guards, or by explicit
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cancellation callbacks if the handler registers them.
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This is a handler-level concern, not a protocol-level one. The protocol's job is
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to cascade the abort; the handler's job is to clean up when cancelled. The
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mechanism (tokio `CancellationToken`, `Drop` guards, explicit callbacks) is a
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two-way door for implementation.
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### 5. The call tree is tracked via `parent_request_id`
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The call tree is already recorded: `OperationContext.parent_request_id` links
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each call to its parent. The cascade mechanism walks this tree to find
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descendants. No separate graph structure is required at the protocol level —
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the `PendingRequestMap` can index entries by `parent_request_id` to enable
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efficient descendant lookup.
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The `@alkdev/flowgraph` package (directed graph with `descendants()`,
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reactive status propagation, `FailurePolicy`) is prior art and may be adapted
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as a separate Rust crate for consumers that need richer call-tree visualization
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or reactive status tracking. It is not required for the protocol-level cascade
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— a parent-indexed map suffices.
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### 6. The abort policy is set on `OperationContext`, not on the wire payload
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The abort policy (`abort-dependents` vs `continue-running`) is set on
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`OperationContext` and propagated to children via `OperationEnv::invoke()`.
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It is NOT a field in the `call.requested` wire payload, and it is NOT a
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per-operation declaration on `OperationSpec`.
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**Why not the wire payload**: the wire caller doesn't know the composition
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tree. The caller of `/agent/chat` cannot meaningfully decide whether
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`/fs/readFile` (composed internally by the agent handler) should survive an
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abort — the handler that composes the child knows that, not the wire caller.
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Putting the policy on the wire payload would give the wire caller control
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over internal composition behavior it can't see.
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**Why not per-operation declaration**: Assumption 5 says the policy
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is per-call, not per-operation. The same operation may need
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`abort-dependents` in one composition context and `continue-running` in
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another. A static property on `OperationSpec` can't express that.
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**How it works on `OperationContext`**: the root context
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(`build_root_context` in the CallAdapter) gets the default policy
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(`abort-dependents`). When a handler composes a child via
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`env.invoke()`, it can specify the policy for that child:
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```rust
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// Default: abort-dependents (child aborts if parent aborts)
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context.env.invoke("fs", "readFile", input, &context).await
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// Opt-in: continue-running (child survives parent's abort)
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context.env.invoke_with_policy(
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"fs", "readFile", input, &context, AbortPolicy::ContinueRunning
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).await
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```
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The child's `OperationContext` carries the policy. If the child itself
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composes grandchildren, the policy **propagates by inheritance** — the
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grandchild inherits the child's policy (which was the parent's policy,
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unless the parent overrode it for the child via `invoke_with_policy`).
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`ContinueRunning` does auto-propagate to grandchildren: if a parent opts
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its child into `ContinueRunning`, and the child composes grandchildren
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without explicitly overriding, the grandchildren also get
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`ContinueRunning`. This is consistent with the composition authority and
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scoped env propagation in ADR-018 — the parent handler decides the
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child's runtime context, including abort policy, and that decision
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propagates through the composition tree by default.
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**Review #002 W19 resolution**: `invoke()` with no explicit policy
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argument inherits the parent's current policy (option a). It does **not**
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reset to `AbortDependents`. A handler that wants a child to reset to the
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default must explicitly call `invoke_with_policy(...,
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AbortPolicy::AbortDependents)`. This makes the propagation predictable:
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the policy I set for my child applies to my child's children unless they
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re-decide. The `invoke()` default in operation-registry.md
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(`abort_policy: parent.abort_policy.clone()`) is correct.
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The `OperationEnv` trait gains an optional policy parameter. The specific
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API shape (a separate `invoke_with_policy` method, a policy field on an
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`InvokeOptions` struct, or a builder pattern) is a two-way door for
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implementation — but the policy enters through `OperationEnv::invoke()`,
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not through the wire and not through `OperationSpec`.
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## Consequences
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**Positive:**
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- No ghost work. Aborting a parent call tears down the entire tree. Resources
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are released, side effects are halted, no results are produced for absent
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consumers.
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- The default (`abort-dependents`) matches the intuitive expectation: if I
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stop caring about the parent, I stop caring about everything it spawned.
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- The opt-in (`continue-running`) covers the legitimate exception (long-running
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work that should survive) without making it the default.
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- The protocol carries cascade semantics, so every consumer inherits the
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correct behavior — no consumer needs to implement its own abort propagation.
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- The `parent_request_id` chain already exists; the cascade mechanism is an
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index on it, not a new data structure.
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- Cleanup hooks are handled by Rust's async drop semantics — dropping the
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handler's future cancels it, and `Drop` guards release resources. This is
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idiomatic Rust, not a custom mechanism.
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**Negative:**
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- The `PendingRequestMap` needs a parent-indexed lookup (a `HashMap<String,
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Vec<String>>` from parent_request_id to child request_ids, or a scan). This
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is a minor implementation cost, not a protocol change.
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- The `call.aborted` event schema carries cascade semantics — clients that
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don't understand cascade (future versions, other implementations) would
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need to handle it. Mitigated: cascade is server-side (the CallAdapter walks
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the tree and sends `call.aborted` per descendant), so clients see individual
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abort events regardless of whether they understand the cascade concept.
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- The `continue-running` policy adds a parameter to the call lifecycle. The
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specific location (payload field, context field, per-operation declaration)
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is a two-way door, but the existence of the policy is a one-way commitment.
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## Assumptions
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1. **Aborting a parent should abort descendants by default.** If the default
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should be `continue-running` (descendants survive), this ADR is wrong. The
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assumption is that ghost work is worse than premature cancellation — a
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cancelled descendant can be retried, but a ghost process consuming
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resources and producing unwanted side effects is harder to recover from.
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2. **The server (CallAdapter) is responsible for cascade.** The client sends
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`call.aborted` for one request ID; the server discovers descendants and
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propagates. If the client were responsible for cascading, it would need to
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know the full tree — which it may not (server-side composition creates
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children the client never saw).
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3. **`parent_request_id` is sufficient to discover descendants.** The call tree
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is a tree (acyclic, single parent per node). If future composition patterns
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create multi-parent relationships (e.g., a shared subcall invoked by two
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parents), the cascade model needs extension. The assumption is that
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composition creates a tree, not a DAG.
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4. **Dropping the handler's future is sufficient for cleanup.** Rust's async
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drop semantics cancel the future and run `Drop` guards. If a use case
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requires explicit cleanup callbacks (e.g., external systems that need a
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signal), the mechanism needs extension. The assumption is that `Drop`
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guards cover the common cases (HTTP stream cancellation, file handle
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release, lock release).
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5. **`continue-running` is per-call, not per-operation.** The policy is
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specified at call time via `OperationEnv::invoke()`, not declared at
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registration on `OperationSpec` and not set by the wire caller. The
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composing handler decides the child's policy based on the specific
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context. See Decision 6.
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## References
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- ADR-015: Call protocol stream model (bidirectional streams, EventEnvelope,
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ID-based correlation)
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- ADR-017: Privilege model (the call tree is the agency chain —
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`parent_request_id` traces principal → agent)
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- OQ-17: Abort cascade semantics (resolved by this ADR)
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- OQ-19: Session-scoped registries (session-scoped operations are in the call
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tree and participate in cascade)
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- `@alkdev/flowgraph` TypeScript package — prior art for call-graph tracking
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with `descendants()`, `FailurePolicy`, reactive status propagation
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- [call-protocol.md](../crates/call/call-protocol.md)
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- [operation-registry.md](../crates/call/operation-registry.md)
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