fix(mcp): correct optional parameter handling

[corylanou]

Description

Correct MCP command construction so optional values use the SDK accessors, empty config paths are omitted, and restore parameters are self-describing. Restore continues accepting the legacy o alias while publishing output, and boolean options now map to valid CLI flags.

In scope:

• Optional MCP string and boolean argument handling
• Empty config omission for every config-aware MCP tool
• Restore output and conditional flag schema descriptions
• Handler-level regression coverage for exact CLI arguments and tool schema

Not in scope:

• MCP version reporting changes tracked independently in fix(mcp): report the running instance's version, not a PATH binary (closes #1353) #1365
• Changes to the underlying Litestream CLI flag definitions

Motivation and Context

Before this change, the regression tests showed databases, info, status, and reset executing with an empty -config value. Restore also ignored the self-describing output argument and emitted boolean values as separate positional arguments. The MCP schema exposed the CLI shorthand o and described conditional behavior as returning an exit code rather than explaining the tool behavior.

Fixes #1366

How Has This Been Tested?

go test ./cmd/litestream -run 'TestMCPToolsOmitEmptyConfig|TestRestoreTool' -v -count=1
go build ./...
go test ./... -count=1
go test -race ./... -count=1
go vet ./...
pre-commit run --all-files
golangci-lint run --new-from-rev=origin/main
GOTOOLCHAIN=go1.25.12 govulncheck ./...

Changed production code is in package main, so the workflow coverage gate is informational; cmd/litestream/mcp.go measured 63.1% statement coverage.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (would cause existing functionality to not work as expected)

Checklist

• My code follows the code style of this project (go fmt, go vet)
• I have tested my changes (go test ./...)
• I have updated the documentation accordingly (if needed)

Closes #1366

[github-actions]

PR Build Metrics

✅ All clear — no issues detected

Check	Status	Summary
Binary size	✅	36.98 MB (+8.0 KB / +0.02%)
Dependencies	✅	No changes
Vulnerabilities	✅	None detected
Go toolchain	✅	1.25.12 (latest)
Module graph	✅	1240 edges (0)

Binary Size

	Size	Change
Base (d26cb54)	36.98 MB
PR (8ac9831)	36.98 MB	+8.0 KB (+0.02%)

Dependency Changes

No dependency changes.

govulncheck Output

=== Symbol Results ===

No vulnerabilities found.

Your code is affected by 0 vulnerabilities.
This scan also found 0 vulnerabilities in packages you import and 1
vulnerability in modules you require, but your code doesn't appear to call these
vulnerabilities.
Use '-show verbose' for more details.

Build Info

Metric	Value
Build time	44s
Go version	go1.25.12
Commit	8ac9831

History (3 previous)

Commit	Updated	Status	Summary
5a0255c	2026-07-18 22:49 UTC	✅	36.98 MB (+8.0 KB / +0.02%)
3ced716	2026-07-18 17:32 UTC	✅	36.98 MB (+4.0 KB / +0.01%)
2bd3a13	2026-07-16 19:58 UTC	✅	36.98 MB (+4.0 KB / +0.01%)

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_{🤖 Updated on each push.}