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[Feature request] Persistent outbox in the companion: retry direct messages until ACKed

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Active
Tech stack
c
Domain
networking

Research direction

Start by reading the related issues #3518, #1489, #1342, and #2974, plus the decision in #613, to understand the existing ACK, retransmission, and TX lifecycle behavior. Then locate the companion firmware’s message handling and companion protocol push code. Done means persistent retry and expiry behavior, deduplication, and outbox state updates work across phone disconnections and intermittent multi-hop reachability.

Written by the indexing model from the issue text.

Description

Goal: a DM is either delivered and ACKed, or reported as expired after a configurable retention time, also when the phone is disconnected and when the recipient is only intermittently reachable over many hops (we measured 4-hop round trips at ~32 km working intermittently, and paths of 8 to 12 hops at ~100 km).

Proposal (endpoint-only, no storage on intermediate nodes, in line with the decision in #613):

  • The companion keeps unACKed DMs in a persistent outbox in flash, instead of relying on the app to retry while connected.
  • Retry policy in the firmware: direct path first, flood with the configured scope after N failures, an immediate retry when an advert or path update from the recipient is received, and backoff otherwise (e.g. 30 s, 2 min, 10 min, 30 min, then hourly) until the retention time expires.
  • The recipient dedups on the existing message identity (timestamp + sender), so a lost ACK and a retransmission do not produce a duplicate in the app.
  • New companion-protocol push codes for outbox state changes (queued, sent, ACKed, expired), so apps can show delivery state even for messages that were ACKed while the phone was disconnected.

Why in the firmware and not the app: the radio is the always-on device and hears the recipient's adverts. App-side retries stop when the phone sleeps (notably iOS background limits) or disconnects.

Airtime: retries are mostly presence-triggered and backed off, so the flood load should stay below what users generate today by resending manually.

Depends on / related to: #3518 (ACK sent for a DM that is then dropped), #1489 (ACK reliability), #1342 (retransmission of direct messages), #2974 (TX lifecycle signalling).

Happy to discuss the design and help with smaller code changes, but I can't commit to building the full feature.

Dominant language
C
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Forks
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Avg merge
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Merged PRs (30d)
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