docs(architecture): add ADR-016 abort cascade for nested calls, resolve OQ-17

ADR-016 locks the abort cascade model:
- call.aborted cascades to all non-terminal descendants via parent_request_id
- Default policy: abort-dependents (abort everything downstream)
- Opt-in: continue-running (started descendants continue, pending ones abort)
- Server (CallAdapter) discovers descendants and propagates; client sends one abort
- Handlers clean up via Rust async drop semantics (Drop guards)
- parent_indexed map suffices for tree walking; flowgraph is optional prior art

Spec updates:
- call-protocol.md abort cascade section references ADR-016
- OQ-17 resolved, ADR-016 referenced across all call crate specs
- README.md updated: ADRs 001-016, OQ-17 moved to resolved

docs/architecture/crates/call/README.md

@@ -30,6 +30,7 @@ Structured RPC over QUIC: operations, request/response, streaming subscriptions,
 | [012](../../decisions/012-call-protocol-stream-model.md) | Call Protocol Stream Model | Bidirectional streams, EventEnvelope, ID-based correlation |
 | [014](../../decisions/014-secret-material-flow-and-capability-injection.md) | Secret Material Flow and Capability Injection | Call protocol carries no secret material; capabilities injected at assembly layer |
 | [015](../../decisions/015-privilege-model-and-authority-context.md) | Privilege Model and Authority Context | `internal` = authority switch not ACL skip; External/Internal visibility; handler identity + scoped env |
+| [016](../../decisions/016-abort-cascade-for-nested-calls.md) | Abort Cascade for Nested Calls | `call.aborted` cascades to descendants; default `abort-dependents`, `continue-running` opt-in |
 
 ## Relevant Open Questions
 
@@ -40,7 +41,6 @@ Structured RPC over QUIC: operations, request/response, streaming subscriptions,
 | OQ-14 | Batch operation semantics | resolved | Correlated `call.requested` events is the correct protocol design |
 | OQ-15 | Call protocol client and adapter contract | open | ADR-014 constrains adapters: credential sources, not static tokens. ADR-015: adapter ops are Internal by default |
 | OQ-16 | Safe vault operations for call protocol exposure | resolved (ADR-014) | None exposed for now |
-| OQ-17 | Abort cascade semantics | open | `call.aborted` cascades to descendants; default `abort-dependents`, `continue-running` opt-in. One-way door on event schema |
 | OQ-19 | Session-scoped operation registries | open | Agent-written operations overlaid on global registry via `OperationEnv` trait layering. Protocol doesn't need changes; one-way door is not closing the trait-based composition point |
 
 ## Key Design Principles
@@ -52,5 +52,5 @@ Structured RPC over QUIC: operations, request/response, streaming subscriptions,
 5. **irpc is one dispatch backend**: Local operations dispatch directly. irpc service calls (in-process, type-safe) are internal. The call protocol is the external interface.
 6. **Local dispatch only**: The operation registry dispatches to local handlers. Remote dispatch (federation, head/worker routing) would be a separate mechanism at a different layer, not a modification to alknet-call's path format.
 7. **No secret material on the wire**: The call protocol carries no private keys, API keys, mnemonics, or decrypted credentials. Handlers receive outbound credentials through `OperationContext.capabilities`, injected at the assembly layer. See ADR-014.
-8. **Abort cascades to descendants**: `call.aborted` for a parent request cascades to all non-terminal descendants. Default `abort-dependents`; `continue-running` opt-in. See OQ-17.
+8. **Abort cascades to descendants**: `call.aborted` for a parent request cascades to all non-terminal descendants. Default `abort-dependents`; `continue-running` opt-in. See ADR-016.
 9. **Internal calls switch authority context, not skip ACL**: The `internal` flag marks composition-originated calls. ACL runs against the handler's identity, not the caller's and not as a blanket skip. Operations have External/Internal visibility. Scoped composition env bounds reachability. See ADR-015.

docs/architecture/crates/call/call-protocol.md

@@ -273,13 +273,13 @@ Local dispatch produces `ResponseEnvelope` with no serialization overhead. The `
 
 ### Abort Cascade and Nested Calls
 
-When a handler composes other operations via `OperationEnv::invoke()`, it creates a call tree: a parent request (r1) spawns children (r1-a, r1-b), which may spawn their own children. The `parent_request_id` field on `OperationContext` records this tree.
+When a handler composes other operations via `OperationEnv::invoke()`, it creates a call tree: a parent request (r1) spawns children (r1-a, r1-b), which may spawn their own children. The `parent_request_id` field on `OperationContext` records this tree — it is the agency chain (ADR-015).
 
-When `call.aborted` arrives for a parent request, the protocol cascades the abort to all non-terminal descendants in the tree. The default policy is **`abort-dependents`**: aborting a request aborts everything downstream, regardless of branch. This is the correct default because aborted parent work has no consumer waiting for results — continuing is wasted work at best and unwanted side effects at worst (e.g., a `bash/exec` that keeps running after the caller stopped caring).
+When `call.aborted` arrives for a parent request, the protocol cascades the abort to all non-terminal descendants in the tree. The CallAdapter walks the tree (indexed by `parent_request_id` in `PendingRequestMap`) and sends `call.aborted` for each descendant. The default policy is **`abort-dependents`**: aborting a request aborts everything downstream, regardless of branch. This is the correct default because aborted parent work has no consumer waiting for results — continuing is wasted work at best and unwanted side effects at worst (e.g., a `bash/exec` that keeps running after the caller stopped caring).
 
-An opt-in **`continue-running`** policy is available for cases where long-running work should survive a parent's abort (e.g., a subscription that should keep streaming). The caller or handler specifies the policy at call time.
+An opt-in **`continue-running`** policy is available for cases where long-running work should survive a parent's abort (e.g., a subscription that should keep streaming). Under `continue-running`, descendants that have already started continue to completion; descendants that haven't started yet are aborted; no new descendants start.
 
-The one-way door is the protocol event schema: `call.aborted` must carry cascade semantics before implementation, because retrofitting cascade onto a non-cascading abort is a breaking protocol change. The mechanism — how the runtime discovers descendants and propagates cancellation (cancellation tokens, parent-indexed map, or a separate graph structure) — is a two-way door for implementation. See OQ-17.
+Handlers clean up resources when their call is cancelled (in Rust, the future is dropped and `Drop` guards release resources — HTTP streams, file handles, locks). This is a handler-level concern; the protocol's job is to cascade the abort. See ADR-016.
 
 ## Constraints
 
@@ -289,7 +289,7 @@ The one-way door is the protocol event schema: `call.aborted` must carry cascade
 - The call protocol is transport-agnostic at the envelope level. The `EventEnvelope` framing can run over QUIC streams, WebSocket frames, or Worker `postMessage`. The `CallAdapter` is the QUIC-specific implementation.
 - `OperationEnv::invoke()` dispatches through the local registry. Remote dispatch (federation, head/worker routing) would be a separate mechanism at a different layer. See ADR-005 and OQ-13.
 - **The call protocol carries no secret material.** Secret material (private keys, API keys, mnemonics, decrypted credentials, raw tokens) must not appear in `call.requested` payloads, `call.responded` payloads, or `OperationContext.metadata`. The wire format carries `serde_json::Value` and cannot enforce this at the type level — the constraint is architectural, enforced by the operation registry and by convention. Operations that need to share public key material use a dedicated operation that returns only the public component. See ADR-014.
-- **Abort cascades to descendants.** `call.aborted` for a parent request cascades to all non-terminal descendants in the call tree. Default policy is `abort-dependents`; `continue-running` is an opt-in. See OQ-17.
+- **Abort cascades to descendants.** `call.aborted` for a parent request cascades to all non-terminal descendants in the call tree. Default policy is `abort-dependents`; `continue-running` is an opt-in. See ADR-016.
 
 ## Design Decisions
 
@@ -302,6 +302,7 @@ The one-way door is the protocol event schema: `call.aborted` must carry cascade
 | Vault integration point | [ADR-008](../../decisions/008-secret-service-integration.md) | Vault is a capability source, accessed at assembly time |
 | Secret material flow | [ADR-014](../../decisions/014-secret-material-flow-and-capability-injection.md) | Call protocol carries no secret material; capabilities injected at assembly layer |
 | Privilege model and authority context | [ADR-015](../../decisions/015-privilege-model-and-authority-context.md) | `internal` = authority switch not ACL skip; External/Internal visibility; handler identity + scoped env |
+| Abort cascade for nested calls | [ADR-016](../../decisions/016-abort-cascade-for-nested-calls.md) | `call.aborted` cascades to descendants; default `abort-dependents`, `continue-running` opt-in |
 
 ## Open Questions
 
@@ -311,7 +312,6 @@ See [open-questions.md](../../open-questions.md) for full details.
 - **OQ-14** (resolved): Batch is a client-side pattern of correlated `call.requested` events, not a protocol primitive.
 - **OQ-15** (open): Call protocol client and adapter contract. ADR-014 constrains the adapter contract: adapters take credential sources from the assembly layer, not static tokens. ADR-015 constrains: adapter-registered operations are `Internal` by default.
 - **OQ-16** (resolved by ADR-014): No vault operations are exposed over the call protocol for now.
-- **OQ-17** (open): Abort cascade semantics — `call.aborted` cascades to descendants, default `abort-dependents`, `continue-running` opt-in. One-way door on the event schema; mechanism is a two-way door.
 - **OQ-19** (open): Session-scoped operation registries — agent-written operations overlaid on global registry via `OperationEnv` trait layering. Protocol doesn't need changes.
 
 ## References

docs/architecture/crates/call/operation-registry.md

@@ -323,7 +323,6 @@ See [open-questions.md](../../open-questions.md) for full details.
 - **OQ-14** (resolved): Batch is a client-side pattern of correlated `call.requested` events, not a protocol primitive.
 - **OQ-15** (open): Call protocol client and adapter contract. ADR-014 constrains the adapter contract: adapters take credential sources from the assembly layer, not static tokens. ADR-015 constrains: adapter-registered operations are `Internal` by default.
 - **OQ-16** (resolved by ADR-014): No vault operations are exposed over the call protocol for now.
-- **OQ-17** (open): Abort cascade semantics — `call.aborted` cascades to descendants, default `abort-dependents`, `continue-running` opt-in. One-way door on the event schema; mechanism is a two-way door.
 - **OQ-19** (open): Session-scoped operation registries — agent-written operations overlaid on the global registry via `OperationEnv` trait layering. Protocol doesn't need changes; one-way door is not closing the trait-based composition point.
 
 ## References