fix(server): fix SQLite enum serialization causing failing test_schedule_lifecycle

[shivros]

Summary

Fixes a failing test on main: test_schedule_lifecycle expected 1 pending schedule but got 0.

Root cause: SqliteStorage used serde_json::to_string() to serialize enum values into SQLite string columns. serde_json wraps enum variants in quotes (e.g. "pending" becomes "\\"pending\\"" in the DB), but SQL queries use bare string comparisons (WHERE status = 'pending'). Writes succeeded but filtered reads returned nothing.

Changes

1. enum_to_str() / str_to_enum() helpers — strip/re-add JSON quotes for SQLite string columns. Applied to unit-variant enum columns: format, workflow_state, schedule status.

2. Platform::to_db_key() / from_db_key() — Platform has a data-carrying Other(String) variant that breaks the generic helpers (serde_json serializes it as {"other":"x"}). Platform gets dedicated DB methods with an "other:<name>" format that round-trips correctly for all variants.

3. cargo fmt — applied to fix pre-existing formatting violations in main.rs and api.rs that would fail CI's cargo fmt --check.

Verification

cargo test          → 8 passed, 0 failed (3 domain + 5 storage)
cargo clippy -D warnings → clean
cargo fmt --check   → clean

New tests added:

• test_enum_round_trip — verifies unit-variant enum serialization
• test_platform_db_key_round_trip — verifies all Platform variants round-trip, including Other("mastodon") and Other("custom:with:colons")

Review Panel

Both reviewers (GPT-5.5, Gemini 3 Flash) initially caught a critical bug: Platform::Other(String) was corrupted by the generic enum_to_str helper. Fixed by adding dedicated Platform::to_db_key/from_db_key methods.

🤖 Generated by Project Runner

[shivros]

🤖 Automated Review Panel

GPT-5.5 (openai/gpt-5.5)

Goal alignment: ✅ The fix correctly addresses the root cause — serde_json::to_string() wrapped enum variants in quotes but SQL queries used bare string comparisons. The enum_to_str/str_to_enum helpers resolve this for unit-variant enums.

Correctness bug found: 🔴 Platform::Other(String) is corrupted by enum_to_str because serde_json serializes Other("foo") as {"other":"foo"}, not "other". trim_matches('"') produces garbage.

Fix applied: Added dedicated Platform::to_db_key()/from_db_key() methods that handle all variants correctly, including Other with an "other:<name>" format. Added test_platform_db_key_round_trip test covering Other("mastodon") and edge cases.

Verdict after fix: ✅ Approve. All variants round-trip correctly.

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Gemini 3 Flash (google/gemini-3-flash-preview)

Goal alignment: ✅ Primary fix is correct and the failing test now passes.

Critical issue found: 🔴 Same Platform::Other(String) corruption bug. The generic helpers break on data-carrying enum variants. Both reviewers independently caught this.

Fix applied: Platform now uses dedicated DB serialization methods. The generic enum_to_str/str_to_enum are only used for pure unit-variant enums (ScheduleStatus, ContentFormat, WorkflowState).

Additional note: The save_content workflow_state column still uses serde_json::to_string for tags — this is correct because tags is a Vec<String>, not an enum.

Verdict after fix: ✅ Approve. All 8 tests pass, CI gates green.

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Both reviewers initially flagged the same critical bug (Platform::Other corruption). Fixed in commit c78f94c before PR was opened.

[shivros]

Auto-Merge Gate — Approved

Confidence: 0.93

Rationale: This PR fixes a clear, well-understood bug: serde_json::to_string() wrapped enum variants in JSON quotes ("\"pending\"") but SQL queries used bare string comparisons (WHERE status = 'pending'). The fix introduces targeted enum_to_str/str_to_enum helpers for unit-variant enums and dedicated Platform::to_db_key/from_db_key methods for data-carrying variants.

Both reviewers (GPT-5.5, Gemini 3 Flash) independently caught a critical Platform::Other(String) corruption bug in the initial approach, which was fixed before PR creation. The fix adds two new round-trip tests covering all Platform variants including edge cases (Other("custom:with:colons")).

Checks observed: ✅ Formatting, ✅ Clippy, ✅ Tests (8 passed), ✅ Build, ✅ Secret Scanning — all green.
Scope: +109/-26, 4 files (platform.rs, storage.rs, api.rs, main.rs). Small, focused fix.
Goal: Fixes test_schedule_lifecycle failing on main. Verified by the new test suite.
No unresolved blocking comments. No "do not merge" markers in Linear or PR body.

Scope limits: This PR fixes the build only — COD-366 (content pipeline implementation) remains pending.

— Auto-Merge Gate (squash)