docs: update Claude Code releases to v2.1.77

- Opus 4.6 default max output raised to 64k tokens; upper bound 128k
- Security fix: PreToolUse hooks bypass of enterprise deny rules
- allowRead sandbox setting, /branch command, /copy N shorthand
- Breaking: Agent tool resume param removed (use SendMessage instead)
- Fixed auto-updater memory leak; fixed --resume history truncation

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

guide/core/claude-code-releases.md

@@ -10,13 +10,13 @@ tags: [reference, release]
 > **Full details**: [github.com/anthropics/claude-code/CHANGELOG.md](https://github.com/anthropics/claude-code/blob/main/CHANGELOG.md)
 > **Machine-readable**: [claude-code-releases.yaml](../machine-readable/claude-code-releases.yaml)
 
-**Latest**: v2.1.76 | **Updated**: 2026-03-14
+**Latest**: v2.1.77 | **Updated**: 2026-03-17
 
 ---
 
 ## Quick Jump
 
-- [2.1.x Series (January-March 2026)](#21x-series-january-march-2026) — Worktree isolation, background agents, ConfigChange hook, Fast mode Opus 4.6, 1M context, claude.ai MCP connectors, remote-control, auto-memory, /copy command, HTTP hooks, worktree config sharing, ultrathink re-introduced, InstructionsLoaded hook, 4 security fixes, Agent model override restored, 12x SDK token cost reduction, /context actionable suggestions, modelOverrides setting, 1M context Opus 4.6 default for Max/Team/Enterprise, MCP elicitation, PostCompact hook, /effort command
+- [2.1.x Series (January-March 2026)](#21x-series-january-march-2026) — Worktree isolation, background agents, ConfigChange hook, Fast mode Opus 4.6, 1M context, claude.ai MCP connectors, remote-control, auto-memory, /copy command, HTTP hooks, worktree config sharing, ultrathink re-introduced, InstructionsLoaded hook, 4 security fixes, Agent model override restored, 12x SDK token cost reduction, /context actionable suggestions, modelOverrides setting, 1M context Opus 4.6 default for Max/Team/Enterprise, MCP elicitation, PostCompact hook, /effort command, Opus 4.6 64k/128k output tokens, allowRead sandbox setting, /branch command
 - [2.0.x Series (Nov 2025 - Jan 2026)](#20x-series-november-2025---january-2026) — Opus 4.5, Claude in Chrome, Background agents
 - [Breaking Changes Summary](#breaking-changes-summary)
 - [Milestone Features](#milestone-features)
@@ -25,6 +25,28 @@ tags: [reference, release]
 
 ## 2.1.x Series (January-March 2026)
 
+### v2.1.77 (2026-03-17)
+
+- **New**: ⭐ Opus 4.6 default maximum output tokens raised to 64k; upper bound for Opus 4.6 and Sonnet 4.6 raised to 128k tokens
+- **New**: `allowRead` sandbox filesystem setting to re-allow read access within `denyRead` regions
+- **New**: `/copy N` to copy the Nth-latest assistant response directly
+- **New**: `/branch` command (replaces `/fork`; `/fork` still works as an alias)
+- **New**: `SendMessage` now auto-resumes stopped agents in the background instead of returning an error
+- **Fixed**: ⚠️ **Security** — `PreToolUse` hooks returning `"allow"` could bypass `deny` permission rules including enterprise managed settings
+- **Fixed**: Auto-updater accumulating tens of gigabytes of memory when slash-command overlay repeatedly opened/closed, triggering overlapping binary downloads
+- **Fixed**: `--resume` silently truncating recent conversation history due to a race between memory-extraction writes and the main transcript
+- **Fixed**: "Always Allow" on compound bash commands (e.g. `cd src && npm test`) saving a single rule for the full string instead of per-subcommand, leading to dead rules and repeated permission prompts
+- **Fixed**: Write tool silently converting line endings when overwriting CRLF files or creating files in CRLF directories
+- **Fixed**: Cost and token usage not tracked when API falls back to non-streaming mode
+- **Fixed**: `CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS` not stripping beta tool-schema fields, causing proxy gateways to reject requests
+- **Fixed**: Bash tool reporting errors for successful commands when system temp directory path contains spaces
+- **Fixed**: Paste being lost when typing immediately after pasting; Ctrl+D in `/feedback` deleting forward instead of exiting
+- **Fixed**: Various rendering fixes: ordered list numbers, CJK bleeding, background colors in tmux, hyperlinks opening twice in VS Code
+- **Fixed**: Teammate panes not closing when leader exits; iTerm2 session crash when selecting text inside tmux over SSH
+- **Breaking**: `Agent` tool no longer accepts a `resume` parameter — use `SendMessage({to: agentId})` to continue a previously spawned agent
+- **VSCode**: Fixed gitignore patterns with commas silently excluding filetypes from `@`-mention file picker; improved scroll wheel responsiveness; improved plan preview tab titles
+- **Performance**: Faster startup on macOS (~60ms) by reading keychain credentials in parallel with module loading; faster `--resume` on fork-heavy sessions (up to 45% faster, 100-150MB less peak memory)
+
 ### v2.1.76 (2026-03-14)
 
 - **New**: ⭐ MCP elicitation support — MCP servers can now request structured input mid-task via an interactive dialog (form fields or browser URL)
@@ -762,12 +784,13 @@ tags: [reference, release]
 | v2.0.58 | Managed settings prefer `C:\Program Files\ClaudeCode` |
 | v2.1.2 | Deprecated `C:\ProgramData\ClaudeCode` path |
 
-### SDK
+### SDK / Agent Tool
 
 | Version | Change |
 |---------|--------|
 | v2.0.25 | Removed legacy SDK entrypoint → `@anthropic-ai/claude-agent-sdk` |
 | v2.1.0 | Minimum zod peer dependency: `^4.0.0` |
+| v2.1.77 | `Agent` tool no longer accepts `resume` parameter — use `SendMessage({to: agentId})` instead |
 
 ### API Ecosystem