fix(sync service): fallback to golden snapshot if no init happens

[404Wolf]

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📝 Walkthrough

Walkthrough

The sync-service durable object gains automatic "golden snapshot" seeding: a new first_uninitialized_connection_at timestamp is recorded the first time a /connect request arrives before the document is initialized. The alarm handler checks this timestamp and, after AUTO_INIT_AFTER (15 seconds), seeds the document with an embedded GOLDEN_SNAPSHOT via a new auto_initialize_golden method. To support this, initialize_handler is refactored to delegate to a new initialize_from_bytes helper reused by both paths. In the cloud-storage service, initialize_existing_markdown gains a 3-attempt retry loop with 1-second delays when calling initialize_from_snapshot.

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 inconclusive)

Check name	Status	Explanation	Resolution
Description check	❓ Inconclusive	No pull request description was provided by the author, making it impossible to assess relevance to the changeset.	Add a description explaining the motivation, implementation details, and context for why this golden snapshot fallback is necessary.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title follows conventional commits format with 'fix:' prefix and is under 72 characters (65 chars), clearly describing the main change of adding golden snapshot fallback.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@rust/sync-service/src/durable_object.rs`:
- Around line 725-738: The doc comment "Gets DocumentState, loading it if
needed" is incorrectly placed above the record_first_uninitialized_connection
function when it should document the document_state function. Move this doc
comment from above record_first_uninitialized_connection to its correct position
above the document_state function. Additionally, add appropriate doc comments
for the new functions record_first_uninitialized_connection and
auto_initialize_golden that accurately describe their functionality instead of
leaving them without documentation.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

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📥 Commits

Reviewing files that changed from the base of the PR and between c1d4a69 and 0e7220d.

📒 Files selected for processing (2)

• rust/cloud-storage/documents/src/outbound/markdown_init.rs
• rust/sync-service/src/durable_object.rs

[coderabbitai]

⚠️ Potential issue | 🟡 Minor | ⚡ Quick win

Misplaced doc comment.

The doc comment /// Gets DocumentState, loading it if needed on line 725 now incorrectly documents record_first_uninitialized_connection instead of document_state (line 740). This appears to be an artifact of inserting the new functions above document_state without moving the existing doc comment.

📝 Suggested fix

Move the doc comment to its correct position and optionally add comments for the new functions:

     Ok(ss)
   }

-  /// Gets DocumentState, loading it if needed
   fn record_first_uninitialized_connection(&self) {
     let mut first_uninitialized_connection_at = self
       .first_uninitialized_connection_at
       .lock("record_first_uninitialized_connection");
     if first_uninitialized_connection_at.is_none() {
       *first_uninitialized_connection_at = Some(web_time::Instant::now());
     }
   }

   async fn auto_initialize_golden(&self, document_id: &str) -> Result<()> {
     info!(document_id, "auto-init: seeding golden snapshot");
     self.initialize_from_bytes(document_id, GOLDEN_SNAPSHOT).await
   }

+  /// Gets DocumentState, loading it if needed
   async fn document_state(&self) -> Result<Arc<DocumentState>> {

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@rust/sync-service/src/durable_object.rs` around lines 725 - 738, The doc
comment "Gets DocumentState, loading it if needed" is incorrectly placed above
the record_first_uninitialized_connection function when it should document the
document_state function. Move this doc comment from above
record_first_uninitialized_connection to its correct position above the
document_state function. Additionally, add appropriate doc comments for the new
functions record_first_uninitialized_connection and auto_initialize_golden that
accurately describe their functionality instead of leaving them without
documentation.