flyby refactors

[Byron]

This happened while trying to push a branch and it seemingly silently skipped doing that and I was very confused.
These changes make it easier to detect the issue.
Also somehow it wanted to pick up a PR template that didn't exist and failed hard because it didn't correctly interpret the return value of a function.
I fixed that, but maybe it causes other issues later if an empty PR template is an issue.

This PR also adds helpers to but-graph to compute merge-bases directly, passing object-ids instead of segment ids. This helps to avoid redoing expensive computations on the Repository later.

[Byron]

This is a CC for @estib-vega due to the PR template change. The question is if it's a problem if it ends up empty. The root issue though is that it thinks there is one in the first place, I couldn't figure out where it has it from, maybe stored state somewhere.

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[Copilot]

Pull request overview

This PR improves diagnosability around branch pushing and review/PR template handling by increasing visibility of push-skip reasons and making template reads more tolerant of missing files, alongside a few tracing/dependency cleanups.

Changes:

• Emit info-level logs when stack branches are skipped during push to make “why didn’t it push?” reasons visible.
• Adjust PR/review template reading to avoid hard failures when template content is missing.
• Reduce instrumentation span verbosity (debug → trace) for some high-frequency operations and tidy an optional dependency entry.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
crates/gitbutler-branch-actions/src/stack.rs	Promotes skipped-branch push logs from debug to info so users can see why a branch wasn’t pushed.
crates/but-graph/src/projection/workspace/init.rs	Lowers Graph::into_workspace span level to trace to reduce default log noise.
crates/but-forge/Cargo.toml	Fixes placement of the optional but-schemars dependency so the export-schema feature can reference it cleanly.
crates/but-db/src/handle.rs	Lowers DB handle construction instrumentation to trace.
crates/but-db/src/cache/handle.rs	Lowers cache handle construction instrumentation to trace.
crates/but-api/src/legacy/forge.rs	Changes template content extraction to default empty content instead of erroring on None.

Comments suppressed due to low confidence (1)

crates/but-api/src/legacy/forge.rs:120

• In review_template, unwrap_or_default() will return Some(ReviewTemplateInfo { content: "" }) even when the configured template file is missing (missing files yield FileInfo::default() with size=None). That makes it hard for callers to distinguish “missing template file” from a legitimately empty template, and it also hides invalid/binary content (where size=Some but content=None). Consider branching on FileInfo.size/content: return Ok(None) when the file is missing, and error (or otherwise signal) when the file exists but isn’t valid UTF-8 text.

            let content = ctx
                .read_file_from_workspace(&path)?
                .content
                .unwrap_or_default();

[Copilot]

Pull request overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (1)

crates/but-api/src/legacy/forge.rs:122

• Same as pr_template(): a review template path that resolves to an image will produce base64 content and mime_type=Some(...), but will currently be treated as valid text because only is_invalid_utf8() is checked. Consider bailing when file.mime_type.is_some() to avoid returning base64 blobs as template text.

            let file = ctx.read_file_from_workspace(&path)?;
            if file.is_invalid_utf8() {
                anyhow::bail!("PR template was not valid UTF-8");
            }
            let content = file.content.unwrap_or_default();