feat(hashline): port hashline edit tool from oh-my-pi

This PR ports the hashline edit tool from oh-my-pi to oh-my-opencode as an experimental feature.

## Features
- New experimental.hashline_edit config flag
- hashline_edit tool with 4 operations: set_line, replace_lines, insert_after, replace
- Hash-based line anchors for safe concurrent editing
- Edit tool disabler for non-OpenAI providers
- Read output enhancer with LINE:HASH prefixes
- Provider state tracking module

## Technical Details
- xxHash32-based 2-char hex hashes
- Bottom-up edit application to prevent index shifting
- OpenAI provider exemption (uses native apply_patch)
- 90 tests covering all operations and edge cases
- All files under 200 LOC limit

## Files Added/Modified
- src/tools/hashline-edit/ (7 files, ~400 LOC)
- src/hooks/hashline-edit-disabler/ (4 files, ~200 LOC)
- src/hooks/hashline-read-enhancer/ (3 files, ~400 LOC)
- src/features/hashline-provider-state.ts (13 LOC)
- src/config/schema/experimental.ts (hashline_edit flag)
- src/config/schema/hooks.ts (2 new hook names)
- src/plugin/tool-registry.ts (conditional registration)
- src/plugin/chat-params.ts (provider state tracking)
- src/tools/index.ts (export)
- src/hooks/index.ts (exports)

src/hooks/hashline-read-enhancer/hook.ts

@@ -0,0 +1,74 @@
+import type { PluginInput } from "@opencode-ai/plugin"
+import { getProvider } from "../../features/hashline-provider-state"
+import { computeLineHash } from "../../tools/hashline-edit/hash-computation"
+
+interface HashlineReadEnhancerConfig {
+  hashline_edit?: { enabled: boolean }
+}
+
+const READ_LINE_PATTERN = /^(\d+): (.*)$/
+
+function isReadTool(toolName: string): boolean {
+  return toolName.toLowerCase() === "read"
+}
+
+function shouldProcess(sessionID: string, config: HashlineReadEnhancerConfig): boolean {
+  if (!config.hashline_edit?.enabled) {
+    return false
+  }
+  const providerID = getProvider(sessionID)
+  if (providerID === "openai") {
+    return false
+  }
+  return true
+}
+
+function isTextFile(output: string): boolean {
+  const firstLine = output.split("\n")[0] ?? ""
+  return READ_LINE_PATTERN.test(firstLine)
+}
+
+function transformLine(line: string): string {
+  const match = READ_LINE_PATTERN.exec(line)
+  if (!match) {
+    return line
+  }
+  const lineNumber = parseInt(match[1], 10)
+  const content = match[2]
+  const hash = computeLineHash(lineNumber, content)
+  return `${lineNumber}:${hash}|${content}`
+}
+
+function transformOutput(output: string): string {
+  if (!output) {
+    return output
+  }
+  if (!isTextFile(output)) {
+    return output
+  }
+  const lines = output.split("\n")
+  return lines.map(transformLine).join("\n")
+}
+
+export function createHashlineReadEnhancerHook(
+  _ctx: PluginInput,
+  config: HashlineReadEnhancerConfig
+) {
+  return {
+    "tool.execute.after": async (
+      input: { tool: string; sessionID: string; callID: string },
+      output: { title: string; output: string; metadata: unknown }
+    ) => {
+      if (!isReadTool(input.tool)) {
+        return
+      }
+      if (typeof output.output !== "string") {
+        return
+      }
+      if (!shouldProcess(input.sessionID, config)) {
+        return
+      }
+      output.output = transformOutput(output.output)
+    },
+  }
+}