fix: reduce context bloat and surface observation masks after pruning

Three generic context efficiency improvements:

1. Surface `observation_mask` for pruned tool outputs in `toModelMessages`
   instead of opaque "[Old tool result content cleared]". The mask was
   already computed by `SessionCompaction.prune()` but never used —
   gives the model post-compaction awareness of what it previously read.

2. Remove dead `<directories>` block from `SystemPrompt.environment()`.
   The tree was permanently disabled via `&& false`, leaving an empty
   XML tag wasting ~30 tokens per API call.

3. Compact skill descriptions in tool schema from 4-line XML per skill
   to single-line `<skill name="...">description</skill>`. Drops unused
   `<location>` URLs. Cuts skill listing size by ~60%.

Includes 8 e2e tests validating all three changes without mocking.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: anandgupta42

packages/opencode/src/session/message-v2.ts

@@ -634,7 +634,9 @@ export namespace MessageV2 {
           if (part.type === "tool") {
             toolNames.add(part.tool)
             if (part.state.status === "completed") {
-              const outputText = part.state.time.compacted ? "[Old tool result content cleared]" : part.state.output
+              const outputText = part.state.time.compacted
+                ? (part.state.metadata?.observation_mask ?? "[Old tool result content cleared]")
+                : part.state.output
               const attachments = part.state.time.compacted || options?.stripMedia ? [] : (part.state.attachments ?? [])
 
               // For providers that don't support media in tool results, extract media files

packages/opencode/src/session/system.ts

@@ -1,5 +1,3 @@
-import { Ripgrep } from "../file/ripgrep"
-
 import { Instance } from "../project/instance"
 
 import PROMPT_ANTHROPIC from "./prompt/anthropic.txt"
@@ -38,16 +36,6 @@ export namespace SystemPrompt {
         `  Platform: ${process.platform}`,
         `  Today's date: ${new Date().toDateString()}`,
         `</env>`,
-        `<directories>`,
-        `  ${
-          project.vcs === "git" && false
-            ? await Ripgrep.tree({
-                cwd: Instance.directory,
-                limit: 50,
-              })
-            : ""
-        }`,
-        `</directories>`,
       ].join("\n"),
     ]
   }

packages/opencode/src/tool/skill.ts

@@ -35,13 +35,9 @@ export const SkillTool = Tool.define("skill", async (ctx) => {
           "Invoke this tool to load a skill when a task matches one of the available skills listed below:",
           "",
           "<available_skills>",
-          ...accessibleSkills.flatMap((skill) => [
-            `  <skill>`,
-            `    <name>${skill.name}</name>`,
-            `    <description>${skill.description}</description>`,
-            `    <location>${pathToFileURL(skill.location).href}</location>`,
-            `  </skill>`,
-          ]),
+          ...accessibleSkills.map(
+            (skill) => `  <skill name="${skill.name}">${skill.description}</skill>`,
+          ),
           "</available_skills>",
         ].join("\n")