fix: resolve state upgrade error for connections with rules (issue #191)

[leggetter]

Users upgrading from v2.0 to v2.1+ encountered a "Value Conversion Error"
with message "mismatch between struct and object: Struct defines fields
not found in object: deduplicate_rule" when configuring connections with
rules.

Root cause: The state upgrader was trying to unmarshal V0 state (which
lacks deduplicate_rule) into the current connectionResourceModel (which
expects it).

Changes:

• Add V0-compatible model structs for state upgrade compatibility
• Update state upgrader to use V0 models and convert to current models
• Add conversion helper functions for V0 to current model migration
• Update getRulePriority to handle DeduplicateRule
• Add unit tests replicating issue Value Conversion Error configuring a connection with a retry rule #191 exactly
• Add acceptance test for V0 to V1 state migration
• Update migration guide with troubleshooting section

Fixes #191

[Copilot]

Pull request overview

This PR fixes issue #191 where users upgrading from Hookdeck Terraform Provider v2.0 to v2.1+ encountered a "Value Conversion Error" stating "mismatch between struct and object: Struct defines fields not found in object: deduplicate_rule" when configuring connections with rules.

Changes:

• Added V0-compatible model structs (connectionResourceModelV0, ruleV0, etc.) that match the schema before deduplicate_rule and response_status_codes were added
• Updated state upgrader to use V0 models when reading old state, then convert to current models
• Added conversion functions (convertV0ToCurrent, convertRulesV0ToCurrent, etc.) to properly migrate state from V0 to V1 format
• Updated getRulePriority to include DeduplicateRule in the correct position (priority 3)
• Added comprehensive unit tests for the conversion logic
• Added acceptance test verifying the issue #191 configuration works
• Updated migration guide with troubleshooting section and workarounds

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/provider/connection/model.go	Added V0 model structs (connectionResourceModelV0, ruleV0, filterRuleV0, filterRulePropertyV0, retryRuleV0) that match the pre-v2.1 schema without deduplicate_rule and response_status_codes
internal/provider/connection/stateupgrade.go	Updated state upgrader to use V0 models when reading old state and added conversion functions to migrate V0 state to current format, including proper handling of new fields
internal/provider/connection/stateupgrade_test.go	Added comprehensive unit tests for V0 to V1 conversion covering retry-only rules, multiple rules, empty rules, transform rules, and filter rule property conversion
internal/provider/connection/resource_test.go	Added acceptance test TestAccConnectionResource_Issue191 that validates the exact configuration from issue #191 works correctly
internal/provider/connection/testdata/issue_191_retry_only.tf	Added test configuration file replicating the exact setup from issue #191
templates/guides/v2.0-to-v2.1-migration.md	Added troubleshooting section documenting the error and providing resolution steps including workaround for users who cannot immediately upgrade
docs/guides/v2.0-to-v2.1-migration.md	Mirror of template file with same troubleshooting documentation

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[Copilot]

@leggetter I've opened a new pull request, #193, to work on those changes. Once the pull request is ready, I'll request review from you.