fix(context): bootstrap group metadata on join when not replicated locally

[chefsale]

[context] Fix group invitation join when group metadata is not replicated locally

Description

Fixes an edge case where joining a group via invitation fails when the joiner's node does not have the group metadata replicated locally. This commonly happens when:

• A group is created without any contexts (no gossipsub topic to replicate through)
• The joiner's node has never been connected to the group's P2P topic

Previously, join_group would immediately bail with:

"group metadata is missing locally; wait for group state to replicate before joining (local governance)"

This was a dead end — the joiner couldn't subscribe to receive group state because they weren't a member yet, and they couldn't become a member because they didn't have the group state.

The fix follows the same bootstrap pattern already used by join_context (lines 210-233 of join_context.rs):

1. When group metadata is missing locally, create stub GroupMetaValue with the inviter as admin
2. Add the inviter as an admin member so governance checks pass
3. Subscribe to the group gossipsub topic
4. Sign the JoinWithInvitationClaim governance op with a zero state hash (since the stub metadata won't match the admin's real state), which the receiving nodes accept per the existing zero-hash bypass in apply_local_signed_group_op

For the non-bootstrapped case (group metadata already replicated), the existing sign_apply_and_publish flow with real state hash is preserved.

Test plan

• cargo check -p calimero-context — passes
• cargo clippy -p calimero-context -- -A warnings — passes
• cargo fmt --check — passes

Manual verification scenario:

1. Create a group (no contexts attached)
2. Create a group invitation on node 1
3. On node 2, join the group using the invitation — previously failed with "group metadata is missing locally", now succeeds by bootstrapping stub metadata

Documentation update

None — this is a bug fix to an internal handler with no public API changes.

  

[meroreviewer]

🤖 AI Code Reviewer

Reviewed by 1 agents | Quality score: 32% | Review time: 99.7s

💡 1 suggestions. See inline comments.

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_{🤖 Generated by AI Code Reviewer | Review ID: review-d74331e2}

[meroreviewer]

💡 Warning log missing group_id for correlation

The warning includes joiner_identity and error but omits group_id, making it harder to correlate with other group-related logs.

Suggested fix:

Add `%group_id` to the warn! fields: `warn!(%group_id, %joiner_identity, %e, "failed to apply...")`