89 validate writer exclusivity for link from at config time

[lxsaah]

Closes #89.

Summary

• Writer-exclusivity for .link_from() enforced at config time. .source(), .transform(), and .link_from() all push into the same buffer; combining any two on a single record was previously accepted and silently degraded to last-writer-wins on latest_snapshot. The configuration now panics with a clear message instead. Extends the existing .source() ↔ .transform() check (aimdb-core/src/typed_record.rs:638,726) to cover the inbound side, closing the gap called out in the issue.
• Symmetric checks across all three setters. set_producer_service and set_transform panic if inbound_connectors is non-empty; add_inbound_connector panics if a source or transform is registered. Same cfg(feature = "std") lock pattern as the existing checks.
• Builder-level pre-check with URL context. LinkFromBuilder::finish() runs the same check via the existing has_transform() / has_producer_service() accessors before calling add_inbound_connector, so the panic message includes the offending URL (e.g. Record already has a .source(); cannot also have a .link_from() for mqtt://broker/topic). The record-level check remains the source of truth.
• Multiple .link_from() on the same record stays allowed. Fan-in (redundant brokers, multi-source ingestion) is a legitimate pattern; only mixing inbound with local writers is rejected.

Tests

Added 5 tests in aimdb-core/src/typed_api.rs:

• link_from_after_source_panics, link_from_after_transform_panics — exercise the URL-bearing panic from LinkFromBuilder::finish().
• source_after_link_from_panics, transform_after_link_from_panics — exercise the record-level panic from set_producer_service / set_transform.
• multiple_link_from_allowed — confirms fan-in is still permitted (two link_from calls, asserts inbound_connectors().len() == 2).

[Copilot]

Pull request overview

Enforces configuration-time mutual exclusion between local writers (.source(), .transform()) and inbound connectors (.link_from()) so a record can’t be configured with multiple competing producers that would otherwise degrade to last-writer-wins.

Changes:

• Added symmetric config-time panics to prevent mixing .link_from() with .source() or .transform().
• Added builder-level pre-check in inbound connector .finish() to produce a URL-bearing panic message.
• Added unit tests covering the new exclusivity rules and confirming multiple .link_from() calls remain allowed.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

File	Description
CHANGELOG.md	Notes the new writer-exclusivity validation behavior at the repo level.
aimdb-core/src/typed_record.rs	Adds defense-in-depth exclusivity checks in set_producer_service, set_transform, and add_inbound_connector.
aimdb-core/src/typed_api.rs	Adds builder-level exclusivity checks in inbound connector finish() and adds tests for the new behavior.
aimdb-core/CHANGELOG.md	Documents the feature addition in the crate changelog.

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