refactor: simplify session log representation

examples/sandbox-acp-agent/tests/acp.snapshot.ts

@@ -35,7 +35,7 @@ const SCENARIOS: Scenario[] = [
   { name: 'config-options', hasModelTurn: false, recorded: false },
   // The runtime mode-switching arc, and NECESSARILY the pinned-header
   // scenario: an approval-policy switch rewrites its prompt section, and the
-  // resulting request/header-delta is legal only in the pinning scenario
+  // resulting changed request/header is legal only in the pinning scenario
   // (the factory's uniformity guard). The pin commits this composition's
   // full header — persona, tool schemas WITH the escalation fields — plus
   // the approval delta and its "changed by the user" notice verbatim. The
@@ -43,9 +43,9 @@ const SCENARIOS: Scenario[] = [
   // sandbox RFC's visibility asymmetry): the recorded arc proves it by
   // BEHAVIOR, a confined write landing under the switched mode with no
   // header change.
-  { name: 'mode-switching', hasModelTurn: true, recorded: true, pinsHeader: true, expectedHeaderDeltas: 1 },
+  { name: 'mode-switching', hasModelTurn: true, recorded: true, pinsHeader: true, expectedHeaderChanges: 1 },
   // The approval wire end-to-end, under the DEFAULT read-only/ask (a switch
-  // would emit a header-delta the uniformity guard forbids here): the
+  // would emit a changed header the uniformity guard forbids here): the
   // escalating bash call streams, session/request_permission attaches to it
   // (allow-once / reject-once), and the scripted answer drives each branch —
   // an approved run executes CONFINED under the granted workspace-write; a

examples/sandbox-acp-agent/tests/snapshots/mode-switching/session.jsonl

@@ -174,7 +174,7 @@
 {"type":"user/message","seq":172,"time":1783613229056,"data":{"content":[{"type":"text","text":"Without using any tools, state your current approval policy in one short sentence and stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"context/message","seq":173,"time":1783613229057,"data":{"content":[{"type":"text","text":"The approval policy changed from \"ask\" to \"never\" (changed by the user)."}],"source":{"kind":"plugin","plugin":"user-approval"}},"surfaceOp":"append"}
 {"type":"step/start","seq":174,"time":1783613229057,"data":{"turn":3,"step":1}}
-{"type":"request/header-delta","seq":175,"time":1783613229057,"data":{"system":{"keepStart":9,"keepEnd":0,"insert":["{{system}}","{{system}}"]}}}
+{"type":"request/header","seq":175,"time":1783613229057,"data":{"header":{"config":{"model":"deepseek-v4-flash"},"system":"{{system}}","tools":[{"name":"bash","description":"Execute a bash command (`bash -c`) and return its stdout/stderr. Each call runs in a fresh shell: no state (cwd, variables, functions) persists between calls — pass `workdir` instead of using `cd`. Non-zero exits are reported as `[exit code: N]`. Commands may run under a file sandbox; a blocked file operation is reported as `[sandbox: file access denied under <mode> mode]` — a policy denial, not a bug in the command; do not retry another way (a background task reports the same marker via bash_output once it has finished). Long output is truncated to its tail; the full output is saved to a file whose path is reported when available. Set `run_in_background: true` for long-running commands: the call returns a task id immediately; poll it with `bash_output` and stop it with `bash_kill`. Attempting a command the sandbox may deny is safe and expected: run it and read the marker rather than assuming the denial. When a command IS denied and a wider mode would let it succeed, escalate immediately in the SAME turn — the ONE sanctioned exception to a denial: retry the exact same command once with `sandbox_permissions` (the narrowest wider mode that suffices) plus a one-sentence `justification`. Do not detour through chat to ask permission first — the approval prompt raised by that retry IS how the user consents. If the session states approval prompts are disabled, there is no exception: a denial is final — do not set `sandbox_permissions`. Never escalate speculatively: ground the request in a real denial — normally the one THIS command just hit; escalating up front is fine only when this session already denied the same access. A rejected escalation is final for THAT command — stop and explain, never work around it — but it does not forbid attempting or escalating other commands later.","parameters":{"type":"object","properties":{"command":{"type":"string","description":"The bash command to execute."},"description":{"type":"string","description":"Clear, concise description of what this command does in active voice, 5-10 words (shown in the UI). Examples: \"ls\" → \"List files in current directory\"; \"git status\" → \"Show working tree status\"; \"npm install\" → \"Install package dependencies\"."},"timeoutMs":{"type":"number","description":"Timeout in milliseconds. The executor applies its configured default and cap, and kills the command on expiry."},"workdir":{"type":"string","description":"Working directory for this command. Defaults to the session workspace; a relative path is resolved against it."},"run_in_background":{"type":"boolean","description":"Run in the background and return a task id immediately. No timeout applies."},"sandbox_permissions":{"type":"string","description":"The wider sandbox mode this command needs. Only valid as a one-shot retry of a command the sandbox just denied; requires justification and user approval.","enum":["workspace-write","danger-full-access"]},"justification":{"type":"string","description":"Required with sandbox_permissions: one sentence for the user explaining why this exact command needs the wider access."}},"required":["command","description"]}},{"name":"bash_kill","description":"Ask the executor to kill a running background bash task by task id.","parameters":{"type":"object","properties":{"task_id":{"type":"string","description":"Task id returned by the bash tool."}},"required":["task_id"]}},{"name":"bash_output","description":"Read new output from a background bash task started with `bash` + `run_in_background`. Returns only output produced since the previous bash_output call, plus the task status. Tasks keep running while you do other work; poll again later for more output.","parameters":{"type":"object","properties":{"task_id":{"type":"string","description":"Task id returned by the bash tool."}},"required":["task_id"]}},{"name":"skill","description":"Load the full instructions for an available skill. Call this with the exact skill name from the session skill catalog before acting on a task that names or clearly matches that skill.","parameters":{"type":"object","properties":{"name":{"type":"string","description":"The exact skill name from the available skills list."}},"required":["name"]}}]},"reason":"change"}}
 {"type":"assistant/chunk","seq":176,"time":1783613230100,"data":{"turn":3,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}}}
 {"type":"assistant/chunk","seq":177,"time":1783613230100,"data":{"turn":3,"step":1,"chunk":{"type":"reasoning-delta","index":0,"text":"The"}}}
 {"type":"assistant/chunk","seq":178,"time":1783613230192,"data":{"turn":3,"step":1,"chunk":{"type":"reasoning-delta","index":0,"text":" user"}}}

examples/sandbox-acp-agent/tests/snapshots/mode-switching/system-prompt.golden.md

@@ -9,7 +9,16 @@ Check the [exit code: N] marker on every bash result; investigate failures befor
 
 <!-- dsh-user-approval-policy:ask -->
 
-<!-- request/header-delta 1: keepStart=9, keepEnd=0 -->
+<!-- request/header change 1 -->
+
+You are an AI agent powered by the DeepSeek Harness SDK.
+
+You are a coding assistant powered by the deepseek-v4-flash model. Your working directory is {{cwd}}. Your bash tool runs under a file sandbox — a `[sandbox: file access denied …]` result is policy, not a command bug.
+
+Verify your work by running the code or tests. Keep answers brief and factual.
+
+
+Check the [exit code: N] marker on every bash result; investigate failures before moving on.
 
 Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`).
 <!-- dsh-user-approval-policy:never -->