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daemon: fold in CORE's sign-off on ADR 0013

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CORE accepted ADR 0013 as written, no amendments
(core/docs/adr-0013-core-response.md, lane/core@c65e664). Folds in:

- pause()/resume() idempotency contract, precisely: no-op success on
  an already-paused task, ALSO on a terminal task (pause racing
  completion isn't an error), resume() no-op on a non-paused task, the
  only error is task_not_found, and no state-change event fires for a
  no-op call.
- tasks_starved pinned as {connecting, downloading} AND
  segments_active == 0 — a structural exclusion of retry_wait and
  auto-paused tasks rather than a special case, with the full state
  table CORE gave.
- restart handling confirmed fully; two non-blocking notes from CORE
  about work-interruption during verifying/assembling.
- "auto-pause" adopted as the term, no new wire/API surface.

Status updated: accepted by CORE; PROTO's item 3 (permit `error` on
event.task.state when state=="paused") is the one remaining blocker
before daemon/src/sched/'s pause/resume logic can be written
correctness-preservingly.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Upd9WhG9oppieig5nRDLig
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sami
2026-09-10 00:05:11 +04:00
co-authored by Claude Sonnet 5
parent 19d3cd2b1d
commit 62cda074c1
1 changed files with 76 additions and 35 deletions
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docs/adr/0013-task-state-machine-ownership.md
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@@ -1,9 +1,13 @@
# ADR 0013 — Task state-machine ownership: CORE, DAEMON, and the shared `paused`
**Status:** proposed · **Date:** 2026-09-09 · **Lane:** DAEMON, drafted at PROTO's request
(D1 in `core/docs/proto-requests-m1.md`), for CORE and PROTO to review and sign off.
**Needs:** explicit accept from CORE and PROTO before `daemon/src/sched/` calls into CORE's
task-start API, since the calling convention below is derived from this split.
**Status:** accepted by CORE, PROTO's open item 3 outstanding · **Date:** 2026-09-09
· **Lane:** DAEMON, drafted at PROTO's request (D1 in `core/docs/proto-requests-m1.md`).
**CORE's response:** `core/docs/adr-0013-core-response.md` (`lane/core`, commit `c65e664`)
— accepted as written, no amendments, plus the pinned `tasks_starved` definition and
`pause()`/`resume()` idempotency contract folded in below.
**Remaining blocker:** PROTO landing the `error`-on-`paused` widening (open item 3) —
`daemon/src/sched/`'s pause/resume logic is unblocked from CORE's side already, but not
buildable correctness-preservingly until that lands.
## Context
@@ -77,19 +81,24 @@ Both sides can put a task in `paused`, for disjoint reasons:
state-change callback — the same path every other CORE-driven transition uses. This is
not a new mechanism.
The contract that makes this safe:
The contract that makes this safe, per CORE's sign-off (`core/docs/adr-0013-core-response.md`):
- **`pause()` is idempotent.** DAEMON calling `pause()` on a task CORE already
auto-paused is a no-op, not an error — DAEMON does not need to know CORE got there
first. Symmetrically, if CORE were ever mid-transition to `paused` when DAEMON's pause
request arrives, the result is still `paused`, once.
- **`pause(TaskId)` is idempotent: a no-op success** on a task already `paused` (however
it got there), and **also a no-op success on a terminal task** (`complete`/`failed`/
`cancelled`) — a pause racing a completion is not an error. **`resume(TaskId)` is a
no-op success on a task that is not paused.** The only error either returns is
`task_not_found`. CORE emits no state-change event for a no-op call — DAEMON reads the
resulting state from the normal state-change callback / `TaskDetail`, never from
`pause()`'s or `resume()`'s return value. If CORE is mid-transition into `paused` (its
own auto-pause) when DAEMON's `pause()` arrives, the task ends up `paused` once, with
exactly one state-change event.
- **DAEMON persists *why* a task is paused**, in the `tasks` table, not in `TaskState`
itself (the wire type stays a flat enum — this is DAEMON-local bookkeeping, not a
contract change). A `pauseReason` distinguishing at least `user`, `schedule`,
`queue_stopped`, `admission_reconcile`, and CORE's `error.code` when auto-paused. This
is what makes §3's resume rule possible — but it needs a contract fix first: see the
gap in open item 3 below. `error.code` is not currently carried on a transition into
`paused` at all.
is what makes §3's resume rule possible — but it needs a contract fix first: see "A
contract gap this ADR surfaces" below. `error.code` is not currently carried on a
transition into `paused` at all.
- **CORE does not need to track why it's paused past the current occurrence.** Once
paused, CORE's job is done; DAEMON is the only side that later decides whether to
resume, and DAEMON is also the only side with persistent storage to remember the
@@ -118,14 +127,28 @@ and asserts `tasks_starved == 0` in steady state past a bounded delay. A task in
`retry_wait` also holds zero segments, deliberately, for up to 60 s (`docs/04` §7's backoff
cap) — and it is **not** admission-starved, it is CORE's own policy holding it idle.
Resolution: `retry_wait` must be distinguishable from true starvation without DAEMON
guessing from timing. CORE's `starved_tasks()` (ADR 0011) excludes any task CORE itself
holds at zero by policy — `retry_wait` and CORE-initiated `paused` both fall outside
`tasks_starved` by construction, because that accessor is about the segment allocator
failing to grant a slot to a task that wants one, not about a task that isn't asking. A
task in `retry_wait` still counts against `connection.maxConcurrentDownloads` from
DAEMON's side (it is running, not requeued) but contributes nothing to the segment
allocator's guarantee pass until it re-enters `connecting`.
**Pinned by CORE's sign-off**, tightening ADR 0011's definition rather than special-casing
it: `tasks_starved` counts only tasks whose `TaskState` is `connecting` or `downloading`
**and** `segments_active == 0` — precisely "the allocator has not granted a slot to a task
that is asking for one."
| Task state | In `tasks_starved`? | Why |
|---|---|---|
| `probing` | no | uses the probe pool (ADR 0011 §5), not the segment budget |
| `connecting`, 0 segments | **yes** | admitted + probed, waiting on the allocator's first grant — the real starvation case |
| `connecting`/`downloading`, ≥1 segment | no | a segment in its own `connecting` sub-state counts as held (ADR 0011 amendment A3) |
| `downloading`, 0 segments | **yes** | held slots and lost them all (e.g. every segment failed and is being re-requested) — transient, still real |
| `retry_wait` | no | CORE's backoff timer holds it at zero *deliberately*; not asking the allocator for anything until it re-enters `connecting` |
| `paused` (either-initiated) | no | not asking for a slot |
| `new`, `queued`, `assembling`, `verifying`, terminal | no | outside the counted state set |
So `retry_wait` and auto-paused tasks are excluded **structurally, by not being in the
`{connecting, downloading}` state set** — not via a special case that could rot as the
engine evolves. `starved_tasks()` returns exactly the TaskIds in this count;
`starved_since(id)` is defined only for them. A task in `retry_wait` still counts against
`connection.maxConcurrentDownloads` from DAEMON's side (it is running, not requeued) but
contributes nothing to the segment allocator's guarantee pass until it re-enters
`connecting`.
### 5. Restart — CORE holds no persistent state, DAEMON reloads to `queued`
@@ -143,6 +166,18 @@ where to actually resume from `.veloxpart.meta` and re-validates with `If-Range`
`paused` tasks reload as `paused`, with their `pauseReason` intact, and are not
auto-admitted — §3 applies identically after a restart as it does live.
**Confirmed by CORE, fully.** `start(TaskId)` transparently checks for a valid
`.veloxpart.meta` sidecar (CORE's stage 5), re-validates with `If-Range` (`docs/04` §5),
and either resumes from the recorded offsets or restarts if the sidecar is missing or
fails validation. DAEMON does nothing special beyond rewriting CORE-owned states to
`queued` and re-admitting, as this section already said.
**Two notes from CORE, not objections to the ADR:** the *transition* into `paused` is
honoured from any CORE state per §1's table, but the *work interruption* is best-effort —
a pause during `verifying` discards the in-progress hash and re-hashes from the start on
resume (cheap, bounded); a pause during `assembling` (HLS/DASH mux) is an M4 concern and
may not be cleanly interruptible mid-mux. Neither changes this ADR's API shape.
## Consequences
- `daemon/src/sched/` calls `start(TaskId)` exactly once per admission (`queued →
@@ -151,10 +186,10 @@ auto-admitted — §3 applies identically after a restart as it does live.
- The `tasks` table needs a `pauseReason` column (DAEMON-local; not a wire type) before
`sched/`'s pause/resume logic can be written correctly — flagging as a concrete
follow-up, not blocking this ADR's acceptance.
- CORE's `starved_tasks()` (ADR 0011) must exclude `retry_wait` and CORE-auto-paused tasks
by construction; if that isn't already true in CORE's accessor, it needs to be before
DAEMON relies on the starvation invariant, since otherwise every backoff cycle would
trip DAEMON's governor-invariant warning as a false positive.
- CORE's `starved_tasks()` (ADR 0011) excludes `retry_wait` and CORE-auto-paused tasks by
construction — pinned in CORE's sign-off as the `{connecting, downloading} ∧
segments_active == 0` definition in §4's table — so DAEMON's governor-invariant warning
will not false-positive on a normal backoff cycle.
- No `contracts/` change. `TaskState`, `event.task.state`, and `previousState` are already
sufficient; this ADR is entirely about which process calls which function when.
@@ -190,15 +225,21 @@ follow-up (minor: widening an existing field's presence condition, per
tell CORE-paused from user-paused on the wire in general — `error: null` on a
DAEMON-initiated pause is sufficient, since DAEMON already knows it just did that.
## Open, for CORE and PROTO to confirm or amend
## Resolution of the four open items
1. Does CORE's `starved_tasks()` already exclude `retry_wait` and auto-paused tasks, or
does this ADR ask for a behavior change there (§4)?
2. Is `pause()` idempotent today, or does calling it on an already-paused task currently
return an error CORE needs to relax?
3. PROTO: land the `error`-on-`paused` widening above before DAEMON writes the resume
logic in §3 — otherwise DAEMON has no correctness-preserving way to implement it and
would have to guess from timing, which is the exact failure mode ADR 0011 was written
to rule out for a different pair of governors.
4. Naming: is "auto-pause" the term CORE already uses internally, or does CORE have an
existing name for this that this ADR should adopt instead of introducing a new one?
1. **`starved_tasks()` excludes `retry_wait`/auto-paused by construction — confirmed.**
Pinned as a design commitment in CORE's sign-off (§4's table above): the counted set is
`{connecting, downloading} ∧ segments_active == 0`, so exclusion is structural, not a
special case.
2. **`pause()`/`resume()` idempotency — confirmed as specified in §2 above**, plus two
details this ADR hadn't anticipated: a no-op call also succeeds against a *terminal*
task (pause racing completion isn't an error), and no state-change event fires for a
no-op — DAEMON reads resulting state from the callback/`TaskDetail`, never from the
call's return value.
3. **Still open — PROTO.** CORE's half is ready (`ErrorInfo` is populated on every
auto-pause transition today's callback path would carry, using the existing B1
taxonomy); the wire only needs `error` permitted when `state == "paused"`. This is the
one remaining blocker on `daemon/src/sched/`'s pause/resume logic.
4. **CORE adopts "auto-pause".** No new wire or API term — the discriminator stays
`state == paused` plus the presence of an `Error` (present ⇒ CORE-initiated, absent ⇒
DAEMON-initiated), exactly as §2 already specified.