Support field-value intent (rationale/confidence/suggestion) in issue_write

[iulia-b]

Summary

Adds per-value intent (rationale, confidence, is_suggestion) to issue field values in the issue_write update path, mirroring the existing labels and type intent support.

Why

Agents setting custom issue field values should be able to attach the same reasoning metadata (rationale/confidence) and mark a value as a suggestion, just like they can for labels and issue types.

Stacked on top of #2663 (type intent). Base this PR on iunia/rationale-issue-write-types; review after the parent merges.

What changed

• issueWriteFieldInput now carries a valueIntent, parsed in optionalIssueWriteFields via the shared parseValueIntent helper.
• resolveIssueRequestFieldValues returns a map[int64]valueIntent keyed by resolved field ID for fields that carry intent.
• Added UpdateIssueOptions.FieldValuesWithIntent and a new issueFieldValueWithIntent marshaler emitting {field_id, value, rationale?, confidence?, suggest?}.
• UpdateIssue's object-form PATCH path now also emits issue_field_values in object form (via issueRequestWithIntentOverrides) when any field carries intent; plain field values stay as {field_id, value}.
• Added the shared intent properties to the issue_fields item schema via withIntentProperties.
• Added Test_IssueWrite_UpdateFieldValuesWithIntent and Test_IssueWrite_UpdateFieldValuesWithIntentErrors; regenerated the affected toolsnap.

MCP impact

• Tool schema or behavior changed
  • issue_write issue_fields items now accept optional rationale, confidence, and is_suggestion. Intent is honored only on update and stripped on create.

Prompts tested (tool changes only)

• "For issue https://github.com/github/planning-tracking-demo/issues/1994 suggest type Task with confidence high and rationale 'testing this for fields too', and Priority field: P1 with confidence medium" — type and field-value intent traveled together in a single update.

Security / limits

• No security or limits impact

Tool renaming

• I am not renaming tools as part of this PR

Lint & tests

• Linted locally with ./script/lint
• Tested locally with ./script/test

Docs

• Updated (README / docs / examples)

[Copilot]

Pull request overview

This PR extends the issue_write tool’s issue_fields update path to support per-field-value intent metadata (rationale, confidence, suggestion), aligning custom field values with the existing intent support for labels and issue types.

Changes:

• Parse and carry rationale/confidence/is_suggestion on issue_fields items, and propagate that intent through field resolution keyed by field ID.
• Add UpdateIssueOptions.FieldValuesWithIntent and emit issue_field_values in object form on PATCH when any field value includes intent.
• Update schema snapshot + add unit tests covering happy-path and validation errors for field-value intent.

Show a summary per file

File	Description
pkg/github/issues.go	Parses field-value intent, threads it through field resolution, and injects object-form issue_field_values into the custom PATCH payload when needed.
pkg/github/issues_test.go	Adds tests verifying request payload shape for mixed intent/plain field values and validates intent input errors.
pkg/github/toolsnaps/issue_write_ff_remote_mcp_issue_fields.snap	Updates the issue_write (FF issue-fields variant) schema snapshot to include shared intent properties on issue_fields items.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 0