Expose executor skills through skill tools (#35184)

## What changed

- Add executor authority support to `skills.list` and `skills.read` for skills from selected capability roots.
- Allow `skills.read` to load package-relative resources referenced by an executor skill while keeping reads within the selected package.
- Paginate skill listings and resource contents with bounded response sizes and stale-cursor validation.
- Resolve executor filesystems per sampling step so skill tools use the active selected capability roots.

## Testing

- Extend the app-server executor skill test to list an executor skill, read its main `SKILL.md`, and read a paginated reference resource.
- Cover visibility filtering, metadata bounds, pagination, invalid cursors, package boundaries, and resource size limits.

GitOrigin-RevId: 1b5de95d5d1b9f79c34d2879d6e67f24401e9c29

codex-rs/core-skills/src/render.rs

@@ -27,14 +27,14 @@ pub const SKILL_DESCRIPTIONS_REMOVED_WARNING_PREFIX: &str =
     "Exceeded skills context budget. All skill descriptions were removed and";
 pub const SKILLS_INTRO_WITH_ABSOLUTE_PATHS: &str = "A skill is a set of instructions provided through a `SKILL.md` source. Below is the list of skills that can be used. Each entry includes a name, description, and source locator. `file` locators are on the host filesystem, `environment resource` locators are owned by an execution environment, `orchestrator resource` locators are opaque non-filesystem resources, and `custom resource` locators use their provider's access mechanism.";
 const SKILLS_INTRO_WITH_ALIASES: &str = "A skill is a set of local instructions to follow that is stored in a `SKILL.md` file. Below is the list of skills that can be used. Each entry includes a name, description, and a short path that can be expanded into an absolute path using the skill roots table.";
-pub const SKILLS_HOW_TO_USE_WITH_ABSOLUTE_PATHS: &str = r###"- Discovery: The list above is the skills available in this session (name + description + source locator). `file` entries live on the host filesystem, `environment resource` entries are owned by their execution environment, `orchestrator resource` entries must be accessed through `skills.list` and `skills.read`, and `custom resource` entries use their provider's access mechanism.
+pub const SKILLS_HOW_TO_USE_WITH_ABSOLUTE_PATHS: &str = r###"- Discovery: The list above is the skills available in this session (name + description + source locator). `file` entries live on the host filesystem, `environment resource` and `orchestrator resource` entries must be accessed through `skills.list` and `skills.read`, and `custom resource` entries use their provider's access mechanism.
 - Trigger rules: If the user names a skill (with `$SkillName` or plain text) OR the task clearly matches a skill's description shown above, you must use that skill for that turn. Multiple mentions mean use them all. Do not carry skills across turns unless re-mentioned.
 - Missing/blocked: If a named skill isn't in the list or its source can't be read, say so briefly and continue with the best fallback.
 - How to use a skill (progressive disclosure):
-  1) After deciding to use a skill, the main agent must read its `SKILL.md` completely before taking task actions. For a `file` entry, open the listed path. For an `environment resource`, use the filesystem of the owning environment. For an `orchestrator resource`, call `skills.list` with `{"authority":{"kind":"orchestrator"}}`, select the matching package, and pass its `main_resource` to `skills.read`. If a read is truncated or paginated, continue until EOF.
-  2) When `SKILL.md` references another resource, use the same access mechanism. Resolve relative paths against a filesystem-backed skill directory. For orchestrator skills, pass the exact referenced resource identifier with the same authority and package to `skills.read`; do not treat `skill://` identifiers as filesystem paths.
+  1) After deciding to use a skill, the main agent must read its `SKILL.md` completely before taking task actions. For a `file` entry, open the listed path. For an `environment resource`, call `skills.list` with `{"authority":{"kind":"executor"}}`; for an `orchestrator resource`, use `{"authority":{"kind":"orchestrator"}}`. Select the matching package and pass its exact authority, package, and `main_resource` to `skills.read`. Follow `next_cursor`; if a read is paginated, continue until EOF.
+  2) When `SKILL.md` references another resource, use the same access mechanism. Resolve relative references beneath an executor skill's returned package and call `skills.read` with the same authority and package. For orchestrator skills, pass the exact referenced resource identifier with the same authority and package to `skills.read`; do not treat `skill://` identifiers as filesystem paths.
   3) If `SKILL.md` points to extra folders such as `references/`, use its routing instructions to identify the resources required for the task. The main agent must read each required instruction or reference file itself before acting on it. Do not delegate reading, summarizing, or interpreting skill instructions to a subagent. Subagents may still perform task work when the selected skill allows it.
-  4) For filesystem-backed skills, prefer running or patching provided scripts instead of retyping large code blocks. For orchestrator skills, use `skills.read` and the available tools; do not invent a local path.
+  4) For filesystem-backed skills, prefer running or patching provided scripts instead of retyping large code blocks. For environment and orchestrator skills, use `skills.read` and the available tools; do not invent a local path.
   5) Reuse provided assets or templates through the same source access mechanism instead of recreating them.
 - Coordination and sequencing:
   - If multiple skills apply, choose the minimal set that covers the request and state the order you'll use them.